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Covid-19

Booster Jabs for Covid-19: What we know and what we don’t?

Two weeks ago the committee advising the UK government on vaccine policy recommended a booster (3rd) dose of a Covid-19 vaccine from September this year with a roll out to protect the whole currently vaccinated population 

By contrast, last week the similar committees advising the USA government stated there was no evidence to support a third dose currently!

Who is right and what is the current level of knowledge about booster doses?

How do booster doses work?

  • Covid-19 vaccines work by stimulating our bodies to produce an effective immune response when faced with the virus
  • This response has both immediate and long term, but more hidden, benefits 
  • The immediate benefit is the production of antibodies to the Covid-19 virus that can be detected in our bloodstream shortly after we have been vaccinated 
  • The longer term, more hidden benefit is the instructions the vaccine gives to the body’s immune system to respond very quickly when an infection strikes us – if you like, it’s like building an immunity production line that just needs to be switched on when the infection happens.  This is called ‘immune memory’ 
  • Not only do we want this ‘production line’ to go into action, but also that it produces a sufficiently large amount of  immunity 
  • Indeed an effective booster dose of a vaccine not only gets the immunity production line ready for action, but using the same analogy enhances its output when infection strikes
  • This is nicely shown in the picture below
https://www.science.org.au/education/immunisation-climate-change-genetic-modification/science-immunisation/3-who-benefits

One or 2 doses of Covid-19 vaccines? 

  • It is now ‘old news’ but the vaccines that are in widespread use (Pfizer, AstraZeneca, Moderna) have all been shown to be much more effective after two doses. After two doses:
    • The clinical data show much greater protection against getting infected and getting seriously ill 
    • The laboratory studies using sophisticated tests have shown that all elements of our immune response (both antibodies and T cells) are much much (deliberately repeating the word!) stronger after two doses
  • Interval between doses
    • Again old news but there does need to be a minimum gap to achieve maximum memory and for Pfizer and Moderna, 3 weeks seems to do the trick
    • The AstraZeneca situation is more complex because of the way they ran their initial trials and it seemed that a 3 month gap produced the best protection – which was plausible – the challenge was the longer wait in the middle of a pandemic to be fully protected 

Why the need for a third dose?

  • Current information is that two doses of the vaccines are effective, both in laboratory and in clinical terms, for at least 6 months 
  • The immediate benefit  of the the immune response, as judged by the measurement of our antibodies, probably declines with time.  
  • The problem is that as the vaccines are still quite new we do not actually know how much that decline might be a problem
  • This is because we don’t know whether the effective immune memory (the ‘production line’) would take over if we became infected 
  • Basically we have no robust data on how effective is the memory part of the immune system beyond 6 months
  • This could be tested in two ways: 

Clinical data 

  • The best test would be to determine how many people who have had 2 jabs develop any/serious infection for the longer term period beyond six 6 months following their second dose.
    • These data will be coming out soon from countries such as England and Scotland and will be compared to those who had not been doubly vaccinated. There are a number of biases in these analyses and they do not take account of any differences in how much exposure to infection people between the vaccinated and non-vaccinated groups

Laboratory data

  • The second helpful study would be intensive laboratory testing of double jabbed individuals after 6 months to see how their immune system would respond in a ‘test tube’ challenge to being infected
    • These experiments could compare the results in samples from people who had  two with those who had three vaccine doses 
  • We do not have such data at the moment (but they should be coming!)

What about the new variants?

  • One of the main arguments behind a third dose booster is that such a vaccine could be more useful against the new variants
  • Remember all the vaccines had been designed to combat the original Wuhan variant
  • Indeed an opinion piece (ie not research based) published by Iranian scientists argued that just giving the same vaccine repeatedly could be more harmful and rather than increase immunity might reduce the development of an effective immune response when a vaccine against new variants is available
  • I do not know in all honesty how likely this is
  • At the moment though all the push in the UK for a third dose is still based on using the original  vaccines
  • The argument being that the current vaccines do work against the new variants* and we do not have a new variant-proof vaccine 

*A study published last year seemed to suggest that the AstraZeneca vaccine was not effective against the Beta (South African) variant, this study has not been replicated and had many problems in the design, so to me that question is still open

What vaccine will be used for any third dose?

  • In brief there are no data suggesting what is the ideal vaccine for any third dose
  • This is especially true as we do not have any specific vaccines that are targeted at the new variants
  • Many studies of having two different vaccines for the first two doses have shown no problems and indeed possibly an even stronger response using a different vaccine second time round
  • Vaccine availability, at the moment, more than anything else will be the driver for third dose vaccine choice, although those with a particularly bad reaction to one of their previous vaccine doses may be offered (or would actively seek!) an alternative  

Special considerations for people with weakened immunity

  • There are several groups with weakened immune systems, either because of diseases like cancer or because of the treatments they are on
  • They have a double challenge:
    • an infection with Covid-19 is much more dangerous
    • vaccines may be less likely to be as effective as in people who normal immune systems
  • Thus
    • Because of the first reason they need to be a priority for vaccination
    • Because of the second, they are more likely to need a booster
  • There was an interesting case of such a person reported in the medical literature recently
    • This person had 4 Pfizer jabs shown by the red blobs (BNT162b2 is posh name for the Pfizer vaccine)
    • Look at the blue line, which is the amount of the main antibody needed to give protection and you can see it was really only after the 4th dose that the antibody level was sufficient to give immunity
https://ard.bmj.com/content/early/2021/06/23/annrheumdis-2021-220834.long
  • It is observations like this, albeit single case reports, that has pushed the Israeli government to go for a third Pfizer dose in such individuals

Is there any argument against a 3rd dose?

  • At the moment we do not have the type of data epidemiologists would want, either on the necessity for a third dose or its timing
  • It could be argued that if not harmful, why wait until proof is obtained, which could be too late to prevent future waves of the infection
  • The ‘original antigenic sin’ argument mentioned above would argue of a potential hazard of using a moderately ineffective vaccine which might make it harder to protect in the future against new variants
  • From a local health service viewpoint, resources (staff etc) devoted to giving a third jab cannot be utilised for other pressing health issues
  • From an international perspective, the rampant infection and low vaccine provision in many low and middle income countries may argue against a third dose in rich countries being a priority

And my conclusion?

  • Sorry but still sitting on the fence on this one!
  • I am sure a third dose (and maybe more) will be needed at some stage but not necessarily as early as 6 months
  • A third dose ideally needs to be designed to be of value for the major variants currently responsible for the majority of cases 
  • A piloted roll out with careful laboratory data collection on how effective a 3rd dose would be after 6 months would be is sensible
  • I would strongly support the Israeli approach of a third dose after 6 months of the current vaccines to those with a vulnerable immune system

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Double vaccinated with Pfizer or AstraZeneca: but how protected am I against new variants?

The initial euphoria following the roll out of vaccines is currently tempered by concerns that their effectiveness is less certain against new variants of the virus.  We now have data from both Pfizer and AstraZeneca vaccines but providing an answer to the question above is quite complex but hopefully this post will help!

New variants for old

  • The vaccines were developed based on the original ‘Wuhan’ strain of the virus and the first clinical trials, proving their success, were in populations exposed to that variant
  • It is obviously relevant to know if those early clinical trial results now also apply to the main current variants, especially the Delta (India) one

A quick comment on the new variants

  • Current focus is on the Delta variant, but there are a number of other variants that are beginning to emerge
  • The data are based on detailed DNA analysis of positive swabs
  • In the main the impact of the variants influences is on how infectious (transmissible) they are, rather than the severity of infection
  • The main reason I give this list with all the newer variants is not to generate anxiety but rather to emphasise that this growing number is an inevitable consequence of the evolution of new mutations during a pandemic
  • There are bound to be other named variants to come – so don’t even bother trying to memorise this list!
  • Although nothing in this pandemic is certain, our knowledge of how effective the vaccines are against the Alpha and Delta strains can probably also be applied to these newer variants 

Five questions to be asked

As someone who has been double vaccinated (with the AstraZeneca vaccine) I assess my risk by considering the following 5 questions:

  1. What is the rate of infection in the population I am exposed to?
  2. How transmissible are the current variants?
  3. How protected is the rest of the population I am exposed to?
  4. Will my vaccine stop me getting infected?
  5. If I do get infected, will my vaccine stop me getting seriously ill?

The answers are of course interconnected but I will deal with them in turn.

1.) What is the rate of infection in the population I am exposed to?

  • It is stating the obvious, but worth repeating, that if the infection rate is very low in my area, then it is less of a worry if my vaccine does not give perfect (100%) protection
  • In this map from last week in England, there was at least a 6-fold variation in the rate of infection between different regions 
To explain: a prevalence of 0.006 is the same as 0.6% of the population is infected
  • I’ve tried to illustrate the impact of this 6 fold variation in relation to my vaccine status in the diagram below, assuming that my vaccine gave me 90% protection. 
  • In an area with a high rate of infection there will be far more cases of infection in both vaccinated and unvaccinated people than in areas with low infection rates
  • The consequence is that the rate of infection in my area is (obviously)  important to my risk of being infected

2) How transmissible are the current variants?

  • Infection rates within a population do not stay static and thus I don’t only need to know what is the current rate of infection, but also is it changing?
  • The figure below comes from English data published this week
  • The top (very light!) grey/purple curve is the curve for Delta and that shows how much more transmissible this variant is than all the other variants analysed

  • Again, even if the vaccines were equally effective against all variants, looking to the short-term future, more vaccinated people will get infected in areas where the Delta variant predominates 

3) How protected is the rest of the population I am exposed to?

  • The hope from the start of the vaccination programme was that not only would I be protected by my own vaccine but also that people around me would have been vaccinated and they would be less likely to get infected and pass that benefit on to me (herd immunity)
  • To be honest it is still not clear how far this is the case.  As discussed below, the vaccines are not perfect against being infected
  • There are good data from populations looking at the trends in the numbers with infection as the vaccination rate increased:
    • For example, data from Israel and the elderly in the UK support that idea that high levels of vaccine uptake might also protect unvaccinated people in those populations
    • Such trends though do not prove cause and effect
  • My conclusion is that even if the vaccines were equally effective against all variants, although I would feel more protected if those around me were also vaccinated, I cannot quantify the change in the level of personal benefit that would bring

4) Will my vaccine stop me getting infected with the new variants?

  • We knew from the early clinical trials (i.e. before the new variants) that the vaccines did stop many people getting infected, but that this was not 100% 
  • Thus these clinical trials suggested that the short term protection was less than perfect for all the vaccines
  • The level of protection was also less with the AstraZeneca than with the Pfizer or Moderna vaccines 
  • We now have data, not from clinical trials but from much larger national population databases, on the effectiveness of the vaccines against the new variants
  • Both England and Scotland have provided such data on this issue
  • They linked:
    • Results from the national testing services which collected information on who tested positive and whether they had symptoms.  These data also gave information on which variant
    • The vaccine status, including data and number of doses and which vaccine 
  • By analysing the data from all the positive tests, they have been able to answer the following question: 
    • How much lower was the rate of infection with symptoms in people who had been vaccinated compared to people who had not been vaccinated?
    • And in particular
      • Was there any difference between AstraZeneca and Pfizer vaccines in this effect?
      • Was there any difference in the effectiveness of the vaccines between the Alpha and Delta variants?
  • This is what they found: 
  • To explain this graph, look at the orange bars (Pfizer vaccine)
    • After two doses of the vaccine, compared to people who had not been vaccinated, the rate of having a symptomatic infection was 
      • 0.06 (or if you like 6%) for the Alpha variant
      • 0.12 (12%) for the Delta variant
  • The figures for the AstraZeneca vaccine were
    • 0.26 (26%) for the Alpha variant
    • 0.33 (33%) for the Delta variant
  • The data from Scotland were similar – for the Delta variant
    • Rates of infection after the Pfizer vaccine rates were 17% of those in unvaccinated people
    •  Rates of infection after the AstraZeneca vaccine rates were 39% of those in unvaccinated people 
  • Actually, these are not that different from the vaccines’ success against the original variant: the Pfizer vaccine has a substantial effect on reducing rate of having an infection the AstraZeneca has a lower effect
  • But this data is less important to me than the risk of becoming seriously ill- next question

5) If I do get infected, will my vaccine stop me getting seriously ill with the new variants?

  • The data came from linking everyone who tested positive and self-reported symptoms with the national hospital record systems 
  • The question then is how far did the vaccines protect against having such a serious infection that they needed to be admitted to hospital
  • However (and this is good news) their first result was that , despite high numbers of people being infected, the absolute numbers of people admitted to hospital were very low and hence the reported effects of vaccination on this may not be very accurate
  • Below are the data from England
  • Again look at the orange bars (Pfizer vaccine)
    • After two doses of the vaccine compared to people who had not been vaccinated the rate of being hospitalised was 
      • 0.88 (or if you like 88%) for the Alpha variant
      • 0.34(34%) for the Delta variant
  • The figures for the AstraZeneca vaccine were
    • 0.53 (53%) for the Alpha variant
    • 0.25 (25%) for the Delta variant
  • These results seem very strange!
    • They suggest that protection against hospitalisation was stronger against the Delta variant than the Alpha variant
    • They suggest that protection against hospitalisation was stronger following the AstraZeneca than the Pfizer vaccine
    • But remember these are based on small numbers 

Combining the answers to questions (4) and (5) together

  • My main question is: will my vaccine stop me getting infected so badly, I need to be admitted to hospital
  • The level of protection will thus be based on how much less likely is it that:
    • I will get any symptomatic infection – and –
    • If I have a symptomatic infection, I will need to be hospitalised
  • The calculation is quite complex and I have shown the details in the box below
  • In summary, these data show that the Pfizer vaccine is 95% effective and the AstraZeneca vaccine is 92% effective against the Delta variant

And the take home message:

  • Apologies, it is a complex question that defies a simple answer!
  • The main messages are
    • Both Pfizer and AstraZeneca (and probably Moderna) vaccines are as effective against the Delta variant as they were against other variants
    • But high rates of infection with the Delta variant, because of its greater infectivity, will mean I am a little less protected than I was when other variants predominate 

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Will my vaccine protect me against the Indian Variant?

First data from Pfizer vaccine.

The Indian Variant (now referred to as ‘Delta’) is recognised as being highly transmissible and, as a consequence, it is now the predominant variant in the UK and elsewhere.  The question in many people’s minds is whether, despite the rising number of cases, those who have been fully vaccinated will still be protected against this variant.  A laboratory study published this weekend in the Lancet suggested that vaccines may be less effective.  This has important consequences both for individuals and communities as to how careful, despite vaccination, we need to be in returning to ‘normal’ life. 

A second concern raised by this study is that the level of protection against this variant after one dose could be much less than against other variants. As vaccine roll out to younger generations is proceeding apace, how much more careful should they be with this variant? Are greater warnings needed not to relax their guard until after their second dose? 

In this post I will try and explain the issues and what the new data tell us

Why we need to understand the background to these variants in relation to current vaccines? 

  • In order to understand why there is now a concern about vaccines and variants, we need to trace the rise and fall of the key variants 
  • The variants of the virus all differ in the shape of its spike protein
  • Importantly they vary in the specific part of the spike protein that allows the virus to enter our cells
  • The Indian variant is the most different in this respect from the Wuhan original virus 
  • Vaccines were developed to produce an antibody response to the spike protein and were designed specifically based on the detailed genetic code for the protein for the Wuhan variant – which was shared worldwide early on in the pandemic by the Chinese
  • The hope from the vaccine developers, even though they could not know what mutations might arise, was that the spike protein of any emergent variants would not be so different that the ‘Wuhan designed vaccine’ would not still work
  • However, the Indian variant is the most different in that part of the spike protein that attaches to the cells in the body, so it is less of a given how much vaccines would work against it

What does ‘how much vaccines work’ mean? 

  • The vaccines all aim that the body produces antibodies against the spike protein of any of the variants
  • These antibodies can knock out (posh term ‘neutralise’) the virus  
  • This is not an all or nothing response with any of the vaccines:
    • All the vaccines should produce some neutralising response
    • The level of this response may vary between the different variants of the virus, as explained above
    • But the vaccines are designed to be very powerful, so just because there is a lower neutralising response against some variants, this does not mean that this would not be  sufficient to stop infection
  • Also importantly individuals will vary in their antibody response because of:
    • Age
    • Gender
    • Health issues including obesity
    • Other factors that are not known 
  • Plus the antibody response may wane over time
  • (not discussed in this post is that – as regular readers will recall – vaccines also work by boosting our T cells to fight infection as well as antibodies – but they are much harder to study!)

What do these new Lancet data tell us:

The study addressed the following questions:

Who did they study?

  • 250 health worker volunteers in London
  • All had had 2 doses of the Pfizer vaccine
  • Their mean age was 42, with just one quarter aged over 52

What did they test?

  • The serum from these volunteers was tested for the level of ‘neutralising antibodies’ (ie antibodies that should stop the infection) at 25 days after the first and 25 and 100 days after the second vaccine dose
  • Antibodies were tested in each serum sample to see if they would neutralise against the following strains of the virus:

1.  Wuhan 

2.  D614G

3.  UK (Alpha)

4.  South African (Beta)

5.  Indian (Delta)

(the Brazilian (Gamma) strain was not tested)

  • They also analysed the antibody responses to compare the results by age, between men and woman  and by body weight 

What did they find?

  • The good news was that only 3% of the participants had no antibodies against the Indian strain
  • Indeed, that percentage was less than the 5% who had no antibodies against the South African strain
  • But, the ability of the antibodies to neutralise the virus  was different when compared between the strains
  • The researchers helpfully presented their data, not just in the levels of antibodies, but more importantly in simple terms ‘how much less good was each sample at neutralising one of the variants compared to the Wuhan’
  • As an analogy think of taking an antibiotic for a throat infection caused by one of 2 bacteria, ‘A’ and ‘B’.  The antibiotic might have some benefit against both types of bacteria but on average be only half as effective against ‘B’ than ‘A’.
  • The researchers in the Lancet study, rather than presenting such a result as ‘half as effective”, preferred to say ‘twice (twofold) as ineffective’ (hope that’s not too confusing!)
  • So here are the data:
  • Thus these vaccinated volunteers had weaker responses to all the strains but they were particularly weaker (nearly 6 times) against the Indian variant
  • But they were also 5 times weaker against the South African variant

Were the results from all people the same?

  • As you would expect, the answer is no
    • Many of the volunteers actually had a good neutralising response to the Indian variant
    • Others had a very weak response
    • On average their response was much lower than against the other variants
  • The older the person, the weaker the response – and that was true against all the variants
  • The more obese the person was, the weaker the response – and again that was also true for all the variants
  • All variants showed a weaker response 100 days after the second dose compared to 25 days

What about vaccine effectiveness after one dose

  • Here the results were more worrying
  • Remember that the first trials of all the vaccines, especially the Pfizer vaccine, showed a good response after one dose
  • Indeed that was the behind the UK government’s decision to increase the delay between doses to 12 weeks – ‘Given the availability and resources to administer the vaccine better to cover twice the number of people with one dose
  • Now look at this figure which I have adapted from the Lancet article: 
  • The black diamonds show the average level of antibodies after 1 and 2 doses
  • As examples I have used red arrows to point to the average values against the Indian variant
  • The top purple line I have drawn shows the ideal level of response, the bottom purple line the lowest level of antibodies that can neutralise the virus: the aim should be to lie between the two lines
  • After two doses, most of the samples were above the minimum in their response –   but lower against  the Indian and South African variants
  • With the Wuhan, D416G and UK variants, one dose of vaccine does provide protection for more than half the volunteers
  • That is not true for the Indian variant, with more than half the volunteers being below the minimal level of response (lower red arrow)

How bad news is all this?

  • As always, need to be cautious!
  • Laboratory samples of antibodies may not reflect what happens in real life in the body when we are exposed to the virus:
    • Antibody levels may increase and could be high enough to neutralise any of the variants
    • T cells may also be active enough 
  • In theory therefore two doses of Pfizer vaccine could still provide sufficient protection against the Indian variant 
  • This may be less likely for older and/or obese people
  • Time will tell the answers to the above – but my guess is that the results of this lab-based study may turn out to be pessimistic 
  • One thing is clear which is that one dose – of what is the most effective vaccine (Pfizer) – does not protect against the Indian variant
  • We need to ensure that younger people, now entering vaccine programmes should not relax their guard until after a second dose!
  • Indeed given these results there is less defence for having a long interval between doses of the Pfizer vaccine 

AstraZeneca or Moderna Vaccine?

These results refer to the data from Pfizer, but it has to be assumed that the conclusions apply to the other vaccines as well

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Our poo – the best early warning system against future waves of Covid-19

Amongst the unsung research heroes for tackling this pandemic have been waste water engineers and geographers.  Examining sewage for traces of the virus has been a truly worldwide effort that is now a key component for managing the pandemic. In this post I address the background and the questions raised by this development. 

How is sewage testing used?

  • Sewage testing looks for evidence that there are cases of Covid-19 infection amongst a community of people 
  • There is a statistically close relationship between the amount of viral fragments found in a sample of sewage and the number of cases in that area
  • In the study below from Canada, the orange bars represent the amount of virus traces in sewage and the blue line the average number of cases
  • Sewage testing can then reveal which areas or communities have high, low  or even absent levels of infection 
  • The street diagram below from Boston in USA shows a map of the sewage pipelines, where the cases occurred and which manholes (the blue circles) should be entered for testing
  • Similarly, sewage testing can also reveal how infection rates in an area change over time
  • In this series of diagrams from Spain, the maps show the changing sewage patterns over the early months of the pandemic and hence where the most cases then emerged

What are the pros and cons of using sewage compared to looking at data from the number of positive swab tests in an area?

  • Sewage testing of course cannot be used for diagnosing individuals or for individual tracing of cases
  • It is however probably superior for  charting infection rates in different areas and communities than local swab test results
  • This is for a number of reasons:
    • The number of people with a positive swab test depends on how many people turn up for testing
    • Thus unless everyone is swabbed there are biases
    • Sewage testing by its nature covers the whole  of that area
    • It is also far cheaper 

What size of population can be tested?

  • The simple answer depends on where in the sewage system the samples are collected
  • Thus, sample collection close  or ‘high up’ in the system has been used in schools and university campuses
  • By contrast sample collection further away can be used in streets/districts and whole towns

If the sewage in my area/community tests negative does that mean there is no infection?

  • There are no guarantees and not every individual, with a current or recent infection, who has provided samples for the laboratory, will pass viral fragments in their stool
  • It is reasonable though to conclude where no viral traces are found in a sewage sample from your area that the likelihood of a significantly risky rate of infection in the community contributing  that sewage is very low
  • More importantly, given the uncertainties in interpreting the swab test data from any small area, I would be more reassured by the absence of virus in the sewage than there were no swab positive cases in my area 

Are the data of the level of viral traces from sewage publicly available?

  • They should and could easily be made as available to the public , in the same way as the number of people with a positive swab test
  • In some countries, such as Netherlands and Australia, these data are on publicly accessible websites
  • This is not yet true for the UK

Will testing sewage be capable of picking up on new variants?

  • Absolutely, the technique is focused on a detailed genetic analysis of the material
  • It is thus probably the most efficient strategy for identifying and then monitoring the spread of new variants
  • Indeed, in one sample of sewage tested in Bristol, they identified 118 different genetic variants

Can you catch Covid-19 from handling sewage?

  • That’s the interesting thing – this appears very unlikely – not that anyone is recommending handling sewage!
  • The viral content in sewage is genetic traces, in the form of RNA and not whole viruses, ie unlikely to be capable of infecting people
  • For the record there have been some laboratory studies which have cultured the virus from sewage but most have been unable to do this

Could this technique provide ‘early warning’ of other serious viral infections?

  • Yes, now the sample gathering processes and testing techniques have been upscaled, it is easy
  • This is now being done in some countries – alooking for early evidence of other viruses such as norovirus (which causes major outbreaks of gastro-enteritis on cruises)

How sensitive is the testing?

  • Difficult to be completely certain, but sewage can show viral traces even if only a tiny proportion of people were infected 
  • One expert suggested that viral RNA could be detected in a sewage system even if there was only one person affected in a system that was ‘served’ by 10,000 people

How quickly would sewage show traces of infection from someone who is infected?

  • This is the interesting result!
  • It seems that sewage is likely to be positive some days before any symptoms develop
  • There are many examples suggesting that the delay between sewage in an area being positive and there being a report of a clinical case is around  5 days
  • Even more fascinating are the data from Italy suggesting that viral RNA was detected in the waste from Milan 64 days before the first clinical case was detected in that city

How long after people had been infected would traces of the virus still be present in sewage?

  • People who had been infected could continue to shed bits of virus material in their stool possibly be for weeks
  • This is not surprising, as we know from PCR tests that viral RNA can still be cultured from swabs long after the infection is passed and the person is neither ill nor infectious

Is there a place not just for testing sewage but testing stool samples from individuals (to replace swab testing)? 

  • In theory stool testing from individuals would pick up that they had viral fragments
  • But the test would not distinguish between active or old infection
  • At an individual level, stools could also be falsely negative when an infection was present so not appropriate for diagnosis or contact tracing for example 
  • There are also considerable and obvious logistic issues in the individual collection, processing and analysis

Conclusion

Worldwide there is now the technology, at an affordable cost, that by the simple act of regular testing of sewage, we now have an early warning system that can monitor how the virus is, and is not, spreading, and with that have the data to help in advising communities about the success of all their policies they’ve introduced to limit the spread of infection

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Indian variant, vaccines and immune escape: what do we know?

Hitting the headlines this week is news about yet another mutant strain, particularly newsworthy because of the accelerating tragedy of the pandemic in India.  This variant is now present in 40 countries. What do we know about this strain, its impact and in particular any possibility that the success of the vaccines could be imperilled?

Is this strain different from other ‘Variants of Concern’?

  • As before, the bit of the virus we are interested in is the spike protein
  • That’s the bit that allows the virus to enter cells and that’s the bit that the vaccines are designed to attack
  • Previous research had shown there were a couple of genetic differences between the ‘natural’ virus (referred to as the Wuhan strain for obvious reasons) and the  other worrying variants such as ‘South Africa’ and ‘Brazil’
  • The ‘Indian’ variant has lots of differences, as shown in the picture below by the code numbers shown in red (Amazing that such a tiny part of such a tiny organism can be so complicated!)
  • Obviously just because there are so many differences, doesn’t mean that any or all of them matter

Any reason that this multi-mutant has arisen?

  • Viruses do mutate all the time 
  • The more the virus reproduces, the more likely it is each time that a mutant can arise
  • In areas with high infection rates such as India, especially with people being quite sick, there are even more reproductions
  • Interestingly some biologists have suggested that often viruses have the ability to weed out mutants that stray from their origins, but Covid-19 is not that careful
  • What we don’t know is how much these new variants would have arisen naturally in any population and how many are brought in
  • The Indian variant may have started life as an import of the UK variant

Is the Indian variant more transmissible?

  • It is quite remarkable how quickly this variant has taken over and seems to be the predominant one across that country 
  • Shown by the arrows:  Kerala in the south, Maharashta in the west, Delhi in the north and West Bengal in the east
  • There has certainly been a phenomenal rise in the number of cases, which can only realistically be explained by the newer variants having a much greater ability to transmit
  • Data emerging from the UK, would also suggest that this variant, like the UK (‘Kent’) variant before, is more transmissible than previous variants

Are cases of the new variant more severe?

  • The brief answer is we don’t know 
  • Laboratory studies on human tissues  suggest that this particular strain is more likely to enter cells lining the lungs
  • Studies on hamsters deliberately infected with different strains showed that the Indian strain produced more severe infection – but not substantially so
  • BUT:
    • Laboratory studies on tissues do not necessarily replicate what happens in whole animals
    • Studies on hamsters may have no relevance for humans (though to be fair it is not unreasonable to do these studies, as it is not ethical to deliberately infect volunteers for the same purposes) 
    • It is not obvious anyway why infection with these strains should be more serious, as opposed to being more transmissible

Will immunity from previous infection protect from the new variant?

  • You may have read the term ‘escape mutant’, which would imply that a previous Covid-19 infection would not protect someone from getting an infection with the new strain
  • There was evidence that prior infection did not protect against the Brazilian variant
  • A study from Germany this week studied the serum from people with a previous infection
    • The study was done entirely based on testing samples in the lab
    • They ‘infected’ these sera with small amounts of either the Indian or the old variant
    • They wanted to see if there was any difference how the existing antibodies in these serum samples would neutralise the infection between these 2 variants
    • They found that these existing antibodies were only 50% as effective against the new variant compared to the old one
    • BUT: 50% might still be enough
    • AND (as above) laboratory studies are not real life

Will the vaccines still protect against the Indian variant?

  • Not surprisingly, we don’t have too much data as yet!
  • There have been some studies on both the Pfizer and the AstraZeneca vaccines
  • For the Pfizer vaccine, I am aware of 2 studies but with quite different results :
    • A study from Cambridge:
      • They tested  serum after one dose of vaccine
      • The sera studied had 80% of the ability to neutralise the spike protein derived from the Indian variant compared to the standard variant
    • A study from Germany:
      • They tested serum after two doses of vaccine
      • The sera studied had only 33% ability to neutralise the spike protein derived from the Indian variant compared to the standard variant
  • For the AstraZeneca vaccine I am also aware of just two reports (which don’t really count as formal research!)
    • The first was anecdotal reports that some health care professionals in Delhi, despite being vaccinated, developed Covid-19 
    • The second was only in the form of a Tweet- reassuring but hardly peer -reviewed – what has the research world come to in only releasing research in Tweets!!!

  • The fact that some of the lab studies suggest that vaccines are less effective against the Indian variant doesn’t mean that they not sufficiently effective – the vaccines have spare capacity in the level of antibodies they produce
  • As regular readers of the blog will know, we also have another part of our immune system – T cells – and even if the antibody response to the new variant is not as strong, our T cells may do the trick (the research to show this is trickier)
  • There is also the reassurance that the vaccines from other laboratory studies are likely to be sufficiently effective against other highly transmissible variants, such as the ‘South African’ one.
  • Finally, given what I have said above, the Indian variant I am sure will be followed by others as the virus continues to mutate and transmit especially in those who are unvaccinated

For further reading and the studies mentioned see: https://www.nature.com/articles/d41586-021-01274-7?utm_source=Nature+Briefing&utm_campaign=9a8cc368a5-briefing-dy-20210511&utm_medium=email&utm_term=0_c9dfd39373-9a8cc368a5-45876838

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High vaccine uptake can control pandemic even with lifting social distancing

That vaccines can protect against Covid-19, in its severe forms, is well established from clinical trials.  Questions remained as to whether (i) when applied to the wider population, these benefits would hold, (ii) vaccines could reduce transmission and asymptomatic infection and (iii) in the ‘real world’ these benefits would be achieved after allowing a return to ‘normal life’.  Data published this weekend in the Lancet from Israel suggests that, at least for the Pfizer vaccine,  the concerns raised by these questions can be discounted

What did we know before this study?

  • In clinical trials two doses of the vaccines achieved a reduction in the risk of contracting severe Covid-19 by over 90% in the 1-2 month period after vaccination
  • There were more modest reductions in the risk of asymptomatic infections, suggesting that the vaccines may be less successful at stopping transmission

What did we want to know?

  • Whether the reduction in severe infections was sustained for longer periods – it was always considered this was likely, but the clinical trials were too short to address this
  • Whether if enough people were vaccinated, the cumulative effect would be to reduce transmission within a community – leading to eventually a greater reduction in asymptomatic cases 
  • Whether premature lifting of social measures, despite high vaccination rates, would increase transmission and ensure the persistence of a ‘pool’ of infected cases within the community

How the Israeli experience can address these unknowns

  • As has been well publicised, Israel has been the leader internationally in the speed of vaccinating its adult population.
  • Only the Pfizer vaccine has been used in Israel and at the recommended 3 week interval
  • There had been a steady roll out of the vaccine programme since the beginning of December
  • By 3 April, 60% of all adults had had two doses, including 90% of those over 65  
  • Israeli public health officials, as part of the ‘deal’ for Pfizer to provide Israel with enough vaccine to cover the country rapidly, agreed to collect data on all the cases of Covid-19 that arose since the start of the vaccine programme
  • The epidemiologists in Israel have therefore been able to compare the risks of developing Covid-19 infection between people who had, and had not, been vaccinated

How did the Israelis do their analysis?

(You can skip this part if you want and go to the results below!)

  • The analysis was quite complex but let me explain what they did
  • The population data were obtained from the 2020 census and thus all adults were included in the analysis
  • Data were gathered on all cases recorded in Israel from 24 January until 3 April 2021
  • Cases of Covid-19 were identified both from the widely and freely available laboratory testing in that country as well as those who were admitted to hospitals
  • It was thus possible to analyse separately the benefits of vaccination on reducing the risk of :
    • Cases with no symptoms (just from testing)
    • Cases with  symptoms but who had not gone to hospital
    • Cases in hospital
    • Cases classified as severe (life threatening)
  • People who had only had one dose of the vaccine, and those whose second dose was less than one week before the end of the surveillance period, were excluded
  • The research thus compared the reduction in the risk of infection between 
    • people who had been vaccinated, at least 7 days after their second dose 
    • people either (i) who remained unvaccinated or (ii) in those who were vaccinated – in the period before their second dose (+7 days)
    • To explain (ii) above consider the diagram below
  • Suppose an individual had completed the course of vaccine on 19th February, so by 26th February they would be considered fully vaccinated 
  • If they had developed Covid-19 in the 30 days up to26th February (the orange period) this case would be counted as having occurred in a non-vaccinated person
  • If they had developed Covid-19 in the 36 days after 26th February up to April 3rd (the blue period) this case would be counted as having occurred in a vaccinated person
  • This person therefore contributed 30 unvaccinated and 36 vaccinated days to the overall analysis
  • The rates of infection could then be compared between the total of ‘unvaccinated days’ and ‘vaccinated days’ in the whole population 

What did they find?

  • The headline result was that the rate of infection in vaccinated people (expressed as cases per 100,000 vaccinated days) was much lower than in people who had not been vaccinated
  • This was as true for very severe cases as for those which had been detected by testing but had not had symptoms
  • The data can also be expressed as the reduction in risk following vaccination: ie how much less in percentage terms were the rates of infection between days after compared to before vaccine (or in those who had had not had any dose)
  • This is what they found:
  • There was an over 90% reduction in all cases, whatever their severity

How do these figures relate to the relaxation of lockdown measures?

  • The helpful diagram below shows on the same chart the path of relaxation of lockdown measures and the rate of cases as reported by the laboratory
  • Israel was going through a serious second wave at the end of the year when the vaccine programme began
  • This was then accompanied by a stringent lockdown as well as the rapid rolling out of the vaccine programme
  • There was a progressive reopening of Israeli society during February, but despite that  the number of cases has continued to fall
  • Given the reduction shown above in the number of cases in the days following  vaccination, it is reasonable to conclude that:
    • Re-opening society clearly did not reduce the impact of the vaccine programme on the number of cases
    • The reduction in the numbers of all cases (ie including asymptomatic cases) suggests that transmission has also fallen again despite relaxation of lockdown and hence widespread vaccination is also leading to an interruption of transmission hastening the end of the pandemic.

Any cautions?

  • The predominant variant in Israel in this period has been the UK variant, so if another variant took hold the results may not be as positive
  • The data only refer to the Pfizer vaccine and for example other vaccines such as AstraZeneca may not achieve the same results
  • As mentioned above it is still early days and we only have 5 months of data; waning immunity following vaccination is still a possibility  
  • Israel is a very mixed society with a large number of ultra-Orthodox who have been at particular risk of infection
    • Indeed there were differences in vaccine rates between ultra-Orthodox and other population groups with only 40% of the former being vaccinated compared to 80% of the remaining Jewish population  
  • It remains therefore to be seen if sub-groups such as the ultra-orthodox will continue to harbour the infection 

Conclusions

  • I believe these data do add importantly to our view about the potential of a successful vaccine programme being capable of ending this pandemic whilst allowing a return to normal life within a reasonable period of time
  • Whether this can be replicated in other countries  remains to be tested in time

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Vaccinating children: arguments for and against

One of the tragic aspects of the news about the escalating pandemic in India is the relatively high proportion of children and young people, not just in the number of cases overall, but also – unexpectedly given Western experience – amongst those with serious infection.  This raises the issue as to the possibility of children being more vulnerable to new variants  and hence whether Western countries need to give greater attention to vaccinating children.  In this post I consider the most recent information and indeed expert opinion on this issue.

Size of the Covid-19 health burden in children 

  • That children also develop Covid-19 in large numbers is not debated
  • The rate of childhood infections is to a great extent related to social mixing at schools and similar institutions 
  • Probably, given exposure to a similar level of the source, children become infected at the same rate as adults
  • Our safeguard from becoming seriously ill with an infection depends on the effectiveness of the ‘first strike immune system’ (referred to as the ‘innate’ immunity we all have in the lining of our noses and throats that protects us against invading bacteria and viruses)
  • Research published this month showed that the innate system is stronger in children and this might explain the lower risk 

Serious infection in children

  • Despite the above, children can still become seriously ill
  • There have, for example, been over 250 child deaths from Covid-19 in the USA
  • The latest data show that 3% of all cases of Covid-19 hospitalised in the USA are in children 
  • It is also established that some groups of children are at particular risk of having bad infection and dying
  • The other health concern is the very strange and rare disorder called ‘multisystem inflammatory syndrome in children’ (MIS-C)
  • Indeed, there have been 3000 cases of MIS-C up to April this year in the USA
  • This severe and previously much less known disorder is difficult to treat and possibly 70% require admission to intensive care, although with adequate treatment mortality rate is only around 2%

What is the state of vaccine testing in  children? 

  • Given concerns about the potential hazard of cerebral venous thrombosis from the AstraZeneca vaccine, this is not I believe being tested further in children 
  • Currently vaccines from Moderna and Johnson & Johnson are being tested and results awaited
  • Data have been published from Pfizer 
    • 2000 adolescents aged 12-15 involved in clinical trial
    • 18 cases of infection occurred in those that had placebo
    • No cases of infection in those who had the active vaccine
    • There were no serious reports of side effects
  • Pfizer want the authorities to license the vaccine for this age group and the result of this application is awaited
  • But  the trial was not large enough, nor could it easily be so, to confirm the necessary safety from serious but uncommon side effects
  • Similarly, given that the cases in the placebo arm were mild or asymptomatic, we do not know how many thousands of children would need to be vaccinated to prevent one serious infection

The ethical arguments for and against vaccinating children

  • One powerful argument in favour is that even the relatively small number of Covid-19 deaths and cases of MIS-C still represents a substantial public health problem
    • Measles vaccine was introduced in the USA at a time when there were 300 deaths a year in children – not too dissimilar from Covid-19 
  • As shown above, there are certain especially disadvantaged groups of children at high risk 
  • In addition, child death rates from Covid-19 are higher in those from certain minority groups – representing an equality issue
  • High vaccine uptake will help ensure full time schooling is more likely and “sellable” to parents
  • The two main arguments against are (i) the low actual risk from the virus, and (ii) the potential of harm from the vaccine
  • Ethically speaking, in  a world where there are vaccine shortages in low-income countries, is there not a responsibility to give vaccines as a priority to adults in those countries?

Herd immunity

  • The main epidemiological question is whether vaccinating children increases the likelihood of herd immunity reducing the risk of infection in adults
  • This raises the ethical question as to  the acceptability of widespread childhood vaccination which is mainly aimed to protects adults – whether or not children will benefit themselves 
  • Put simply – “will the virus disappear more quickly if children are vaccinated?” or indeed the converse “will the virus still be around if we don’t vaccinate children?”, as outlined in a recent New York Times leader
  • There is no proof of this however
  • Indeed, data from Israel would seem (thus far) to suggest that herd immunity – as exemplified by the number of new cases dwindling to almost none – might be accomplished without vaccinating children 
  • A related biological argument is that if children are not vaccinated, is there a risk that new variants will arise in children that will then spread to vaccinated adults, whose vaccine status is not sufficient to protect them against such variants 
    • Whilst such an argument is superficially persuasive, there are no data (as yet) to support it
    • Many expert virologists have struggled to find evidence that this has happened with other viral infections and vaccines 
  • The second question which is the converse of the above is whether we don’t need to vaccinate children as they benefit from the herd immunity provided from high rates of vaccinated adults 
  • Data (also from Israel) this month would support this: population surveillance of new cases suggest that the increasing rates of vaccination in adults have seen a parallel reduction in cases of infection both in adults and in children 
  • In other words the lower rates of infection in children may be explained by the protection from high rates of vaccine uptake in adults
    • But it is only recently that lockdown has been relaxed in Israel  and children have returned to school – so if there had been a surge, it would not have been picked up by this research study
  • Similar data from the USA have shown that a reduction in the number of cases in adults, which is thought to be partially explained by vaccine uptake in adults, is also mirrored by a similar reduction of cases in children 

And my conclusion?

  • This is really difficult, for the reasons I have stated 
  • So, it is not surprising there is not a clear cut conclusion to be drawn at this stage
  • The vaccines are probably as safe as is reasonable, so that supports childhood vaccines
  • Children may indeed be protected by high rates of vaccination in adults 
  • It is much less obvious that high rates of vaccination in children will protect adults 

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Why social distancing will be needed even after vaccination, despite the experts disagreeing!

As vaccination progresses in most countries, there is still the concern that although the vaccines protect against severe infection, they are less successful in preventing transmission, especially with the so-called “variants of concern”.  Yet experts are even this week arguing as to what is the most important route for catching the virus.  Public confidence and adherence to appropriate social distancing need them to be singing (but not too loudly!) from the same song sheet. (And that song might just involve cucumbers – see the end of this post!)

Aerosol or droplets as main route of infection?

https://www.gaiadiscovery.com/planet/covid-19-aerosol-transmission-hospitality-tourism-implications
  • Readers I am sure will remember the discussion about whether Covid-19 is transmitted by large droplets or can be carried much further in the air as an aerosol 
  • Handwashing and social distancing to a metre are considered sufficiently protective against droplet transmission 
  • Indeed by 2 metres droplet transmission is unlikely 
  • Hence at the beginning of the pandemic the World Health Organisation (WHO) at their infamous press conference argued against the value of face masks
  • WHO suggested that aerosol transmission was not an important route as Covid-19 was not airborne 
  • That opinion delayed widespread mask wearing and did not discourage social distancing beyond that short distance
https://www.weforum.org/agenda/2020/03/who-should-wear-a-face-mask-30-march-who-briefing/
  • Much of the data for airborne transmission came from experiments in the laboratory trying to recreate what happens in life
  • The argument was that the virus can transmit via the airborne route in the laboratory does not tell us how important that route of infection are in explaining who gets and who does not get infected 
  • But if airborne infection is the most likely route then too rapid a reduction in social distancing and mask wearing regulations could contribute to further surges in infection

World Health Organisation: are they wrong again?

  • At the end of March this year a review of the available data, funded by WHO, suggested that airborne transmission could  not be proven 
  • In that paper, which was widely publicised before peer review, Heneghan (from the Centre for Evidence Based Medicine at Oxford) and colleagues reviewed 90 research articles which had attempted to discover if Covid-19 could be airborne
  • They applied their own stringent criteria to assess the quality of those research  studies
  • They rejected a firm conclusion because the quality of the research was not considered high enough
  • As an epidemiologist I am (of course!) in favour of research being high quality, but such reports need to be careful in dismissing something as important for public health as this issue
  • Indeed in the past 24 hours, the initial peer reviewers’ comments have just been posted and are not looking too good!

What is the evidence in favour of airborne transmission?

  • Given the publicity for that WHO report there has been an rapid riposte.
  • In an authoritative paper published in the Lancet a week ago, another colleague from Oxford, Trish Greenhalgh, gave 10 pieces of evidence which I believe would stand up in a court of law as proving more likely than not that airborne transmission was the key route of transmission
  • These were her points:
  1. Superspreading events such as on cruise ships and choirs can only be explained by that route
  2. Transmission of infection between people isolating in their rooms, across corridors for example in those quarantined in hotels 
  3. Perhaps as many as 1 in 3 of cases are transmitted from asymptomatic  people who are not coughing or sneezing, and not passing out large droplets 
  4. Transmission of SARS-CoV-2 is far higher indoors than outdoors and is substantially reduced by indoor ventilation
  5. Hospital and care home acquired infections have occurred  despite very  strict precautions against droplet spread and the limited effectiveness of much  personal protective equipment (PPE) – which is designed to protect against droplet but not aerosol exposure
  6. Laboratory studies have shown that the Covid-19 virus can survive in the air and be infectious for up to 3 hours
  7. The Covid-19 virus has been found in air filters and building ducts in hospitals with COVID-19 patients
  8. Studies of infected caged animals which were connected to separately caged uninfected animals via an air duct and then caught the infection 
  9. The data from contact tracing and interviews of infected people found no other convincing route of infection other than airborne
  10. Finally, although Heneghan and colleagues might argue against the quality of the research proving airborne transmission, the opposite has not been proven – that airborne transmission does not occur  

The conclusion in that Lancet article is worth repeating here:

And the role of cucumbers:

  • No this is not April 1st!
  • Research published this week looked at how long the virus survived on various fresh fruit and veg food items that were unlikely to be cooked 
  • They inoculated test areas of the surface of these foods with the virus and measured the concentration of the virus on the surface at various subsequent time points
  • Concentrations in terms of the number virus particles fell from the thousands over the next few hours
  • As shown in the diagram, the virus had gone from apples and tomatoes within 16 hours but was still present on cucumbers at 72 hours
  • Of course there are no data to suggest that cucumbers are in any way a likely source of infection, though interestingly the pH of the surface of cucumbers is more friendly to viral survival
  • And remember you saw this important result on this blog first! 

Take home message

I mention the cucumber study not because it is of major importance to the spread of infection. Rather to illustrate my main point that, especially in this pandemic, it is so important to judge all the research ‘in the round’

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New wave despite vaccine success: how likely/how large?

Vaccine roll out success, coupled with adherence to behavioural rules, has led to substantial declines of infections in the UK and Israel.  Increasing vaccine coverage in North America and Europe is seen also as the route back to normality.  Yet infectious disease epidemiologists are still worried about a third wave causing large numbers of severe cases.  Are they right to be worried?

Let’s start with the current success

  • Excluding countries in the Far East and Australasia, globally most other countries have had substantial second peaks of infection
  • I have plotted below the rates/million total population (including children) of new diagnosed infections in Israel and UK 
  • The UK – with one of the most stringent and (probably) adhered to lockdown measures since the start of January – has seen a substantial fall in the rate of new cases.  Given that only around 10% of the population has had a second jab, then the decline in new cases is predominantly explained by the measures enforced
  • Israel has a second jab rate of around 60% and epidemiological studies, examining the vaccination records of those who have become ill, by contrast, do point to vaccine roll out being the major explanation for the decline
  • Indeed Israel began easing its lockdown rules in mid-February without seeing, so far, any rise in the rate of infection 

So what’s the worry?

  • Worth repeating (and I have!), though obvious – if we all stayed at home then the infection would die out.  So whether the rates of new infection are going to remain controlled as lockdown is released depends on a number of factors
  • I have illustrated these in the diagram below and will consider them all in turn
  • The general point is that we need to consider a range of factors in order to achieve the elimination of the threat of Covid-19 

Vaccine effectiveness

  • In terms of transmission we want the vaccines to stop people being able to pass on the infection those around them
  • We know that the vaccines stop people getting ill, but it is still uncertain by how much the vaccines stop people transmitting the infection
  • Here are some estimates from two epidemiology groups from the UK: Imperial College London and Warwick University
  • ‘All infections’ includes those with and without symptoms 
  • The rates of infection are following the second jab and assume no waning in immunity over time
  • The assumption about waning immunity is probably reasonable over a short time frame, i.e. protection at least until the end of this year
  • These figures are from the rolled out vaccination programmes rather than the earlier clinical trials and are estimates of the effects across all adult age groups 
  • Pfizer probably stops 90% of transmissions and AstraZeneca around 60%
  • A 60% reduction in transmission though is really good if the population rates of infection are low.  Conversely if the population rates of infection are high then, even with a 90% reduction, there is still scope for high numbers of new infections to be passed from vaccinated people

Vaccine coverage

  • Thus far in Israel, UK and USA, the vaccine coverage has been higher than the pessimists feared
  • Concerns about hazards and the roll out to younger populations less at-risk from severe infection might see a decline in take up, although restrictions on travel etc for those without a vaccine might encourage greater take up
  • Based on different sources of data here are the projections (OK they are guesses!) of vaccine take up in the UK:
  • Although these figures seem ‘very good’, as with the effectiveness data above, in periods of high infection even 10% of people who are not vaccinated could contribute to a large number of people being susceptible to infection

Speed of vaccine roll out

  • Again obvious, but the longer it takes to vaccinate the population the greater the number of people who can transmit the infection
  • This is because as mentioned above  vaccinated people, even with a pessimistic (AstraZeneca) protection, are 60% less likely to transmit the infection
  • An interesting ethical issue is that younger people have more social contacts and currently in many countries contribute proportionately more cases of infection than older people
  • Thus it could be argued that to prevent transmission alone, it might make some sense to focus vaccine efforts on those who are younger 
  • Anecdotally this may be what is happening  in some countries in Eastern Europe

Seasonality

  • As is well known, influenza pandemics tend to occur in winter
  • Whether this is because in the summer there is reduced viral survival with the greater  sunlight and/or humidity, or we spend less time outdoors, is unknown
  • The concern from some epidemiologists is that the decline observed now in countries such as the UK may represent a seasonal decline and that come winter there will be a bounce back 
  • This is the effect of season from the Warwick and Imperial guesses
  • These are not large differences but could tip the balance
  • This underlines the importance of achieving high vaccine coverage before the autumn

Impact of new variants

  • It is now well known that the current major variant in UK, USA, Israel and indeed the rest of Europe is the so-called English variant
  • This variant does spread more easily
  • The South African variant also spreads even more easily, but it seems that high rates of the English variant seem to reduce the South African (or indeed the Brazilian) variants from taking a major hold
  • The epidemiologists have in their scenario planning assumed that no new nastier variant will take hold – this is probably reasonable but cannot be relied on absolutely

Social Behaviours 

  • Clearly a return to normal social interchange increases the chances of transmission
  • It was believed at the start of the pandemic that the natural R value, i.e. the average number of cases caused by one person passing it on to others, is around 2.5
  • Countries with their various lockdowns are achieving rates of say between 0.8 and 1.5
  • R values have to be considered against how many cases there are of course, but the worry is that releasing the brakes given all the other issues mentioned above could lead to a greater number of new transmissions.

Putting it altogether

  • Complicated isn’t it!!
  • This is just one model from Warwick attempting to predict the number of cases hospitalised in a third wave this summer: 
  • To be honest they’ve brought so much together in that graph that I’m not going to even try and explain it all ! But there is an important message here
  • The red line has allowed for all the things I have mentioned above (they call it the ‘central assumption’)
  • An increase in R because of any of the issues mentioned would have major effects on the numbers of severe cases (in this graph shown as the how many beds in hospitals in the UK are occupied by Covid-19 patients) 
  • We can’t easily change the effectiveness of the vaccines (they are pretty good), the seasonal impact or the possibility of new variants
  • By contrast, we can ensure maximum and speedy vaccine coverage
  • More importantly, it will be necessary to keep tabs on all the above, to ensure that any return to ‘normality’ is carefully monitored

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New calculation: Risks from AstraZeneca vaccine exceed benefits in people under 30

In my post earlier today, I stated that “it is possible that the risks of cerebral venous sinus thrombosis in younger women are greater than the risks from Covid-19 infection”.  This afternoon, the regulator in the UK announced the results of their detailed calculation addressing this question.  

This is the result of their calculation and I have adapted their slide for this post

copied from presentation given at press conference by MHRA 7th April
  • This is how they did their calculation
  • First they obtained the current rate of new Covid-19 infections in the population.
  • They then identified how likely it was that someone with a new infection would be admitted to an intensive care unit (ICU)
  • They analysed these data by age
  • They then calculated how many people per 100,000 in each 10 year age group would be admitted to an ICU in a 16 week period  at that rate of infection
  • These rates (the blue boxes) were very low for those age under 30 at less than 1/100,000,  but were much higher for those aged 60-69 at 14/100,000
  • They then calculated what the rates of serious harms would be in those who were vaccinated based on the numbers and ages of the cases reported to date
  • They then estimated how many people per 100,000 who had been vaccinated with one dose would have a serious clotting problem
  • They estimated these rates separately for each 10 year age group would
  • The rates of vaccine problems were highest – at 1/100,000 in those under 30 and lowest at 0.2/100,000 in those 60-69
  • Putting all this together the conclusion is that
    • In those aged 20-29, the risks from the virus and those from the vaccine were similar
    • In those aged 60-69, the risks from the virus were 70 times (ie 14.1 divided by 0.2) higher than those from the vaccine
  • In most other European countries the rate of infection is much higher than in the UK
  • The higher the rate of infection and the more the number of people get infected then more get admitted to ICU, whereas the risks from the vaccine remain the same
  • The consequence is that as the incidence of infection rises, (it is obvious really), the benefits from the vaccine relative to the harms becomes more favourable 

My conclusion:

  • Given the low rates of current infection in the UK it makes sense to use alternative vaccines in those aged under 30
  • The European Medicines Agency has not issued the same advice, they may do so of course in the near future, but with the higher infection rates in EU countries, the benefits from the vaccine are still present for all age groups 

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