Covid-19 Masks

Face masks: Is there a lesson from the Plague 400 years ago?

Whilst researching the value of face masks I came across some of the thoughts about containing the epidemics of the Plague that swept through Europe in the Middle Ages and Early Modern times.  Hope you might find it interesting to see that the same questions were asked then (and with a Shakespearian connection!)

Source: Deathsplanation

What is the plague?

  • Infection by flea carried by rats of the bacteria Pasteurella pestis
  • Nasty infection causing typical swellings and pneumonia 
  • Can spread by droplets from an infected person
  • Caused millions of deaths 

What was thought about the cause of the disease

  • Of course no one knew about the bacteria that caused the disease
  • There was much superstition about evil spells
  • Main concern was that the disease spread through the bad air or ‘miasma ‘surrounding an infected person 

Origins of quarantine

  • In  middle ages there was concern that plague could spread
  • Ships in Venice with cases of plague had to isolate at anchor for 40 days (hence the word quarantine)
  • Most famous case in England was the village of Eyam in Derbyshire where 260 villagers who self-isolated died but protected thousands from surrounding villages 

The first face masks

  • To prevent breathing in the bad air physicians at the time wore, what we might call today hazmat suits
  • They were made of leather and covered with wax
  • The characteristic mask had a beak (with herbs to prevent infection)
  • The beak had a hole at the end to allow breathing
  • Some medical historians thought the design was to scare  the evil spirits but others believe that the need for a physical barrier was understood
  • Physicians also had a long stick, so that they could stand on the doorway and poke away the patients’ clothes, to see the swellings  without having to touch them!

And the Shakespearian connection!

Coincidentally I am reading the new novel, Hamnet by Maggie O’Farrell.  The novel reimagines the sad story of Shakespeare’s son, Hamnet (almost certainly the source of the play Hamlet) who died of the plague aged 11 whilst dad was away being famous in London.  Last night I came across this dialogue:

A physician in full mask has come to visit Hamnet’s sister who is very ill with plague, Hamnet is very scared by this man and asks his mother

….”But why is he…?” Hamnet gestures to his (the Physician’s) face, his nose

“He wears that mask because he thinks it will protect him” she says

“From the pestilence?”

His mother nods

“And will it?”

His mother purses her lips and shakes her head

“I don’t think so.  Not coming into the house however, refusing to see or examine the patient, might” she mutters!!!

Discussion of the scientific data to address this will come in the next blog post!

Covid-19 Masks transmission

Face masks 2: How effective are cloth face masks?

Face masks covering the nose and mouth are designed to act as a barrier to reduce viral spread. If people who are infected wear a face mask, is that enough to stop them infecting other people? In this post I review the evidence that the wearing of ‘normal’ cloth face masks is a good enough barrier to prevent passing infection to others.

To recap from my post last week:

In my first post on face masks last week, I posed the key question: “How much can the widespread  wearing of face masks reduce the spread of infection in the population?”  I argued that even if everyone wore face masks, the number of new cases in any area  would also depend on several other factors:

  1. The effectiveness of the chosen masks as a barrier to passing on the virus
  2. The safe and appropriate use of any face masks worn 
  3. The level of adherence to other mitigation measures such as social distancing, hand washing etc
  4. The background risk of infection in a local population. 

In this post I address the first question, on the success or otherwise of face masks as a barrier to the passage of virus

Who is protecting whom?

Source: Mario Tama/Getty
  • The research on the effectiveness of face masks as a barrier is based on studying how they stop the virus spreading from an infected person. 
  • It is very difficult (ethically and logistically) to do a study  to show that wearing a face mask is an effective barrier to receiving the virus from an infected person
  • It is a reasonable assumption that the barrier is equally effective in both directions  – although the receiver can also get infected via the eyes or passing droplets by hand to their nose or mouth

Surgical masks

  • Much of the research is on the effectiveness of surgical masks and their use in health care settings
  • Surgical masks have non-woven fabrics (no holes) and are disposable 
  • Several studies show that surgical masks are very effective at reducing the risk of infection
  • As an example, research  from Hong Kong published in May studied people all of whom had a positive swab test either for Covid-19 (or  for common cold or flu).
    • They then studied the proportion of those people who were breathing out viruses, both without and with a face mask.
    • They measured if there was shedding of the virus in both large droplets and small droplets (aerosols*)
    • Of those with CoVid (blue bars in graph below), who did not wear a face mask,  30%  shedded virus as droplets and 40% as aerosols.
    • With a face mask none of those with Covid-19 shed the virus in either form
    • Interestingly in this study, surgical masks were more effective as a barrier to Covid-19 than to the common cold or flu viruses

What about cloth masks?

  • Disposable surgical masks are not a practical proposition for use in the general  population
    • The number of masks needed would be enormous
    • The cost for individuals or organisations is excessive
    • They are not comfortable for wearing for long periods such as a school or working day
  • In SARS and in other pandemics, authorities had suggested that cloth masks are the only feasible alternative for the general population who are not at the same risk as say health care workers
  • Several previous research studies, from SARS 1 and other epidemics, have shown that surgical masks are far superior to cloth masks, but might cloth masks be good enough?

Challenges in assessing the value of cloth masks

  • For sure it is more difficult to block aerosol spread than droplet spread in woven cloth materials even if we can’t see the holes
  • Holding up a mask to the light and seeing if nothing shines through is helpful but this is not proof it would filter out the smallest droplets
  • It is also clear that the likelihood of transmission of virus even through a well-fitting cloth mask is increased by:
    • the amount of virus
    • how much speaking/shouting/coughing etc takes place
  • Thus, it is really difficult from the available research to be definitive about how effective cloth masks are as a barrier.

There are cloth masks and cloth masks!

  • There are several designs of cloth masks which make it difficult to draw conclusions about cloth masks in general 
  • Factors that vary include:
  • Number of layers
  • Shape: conical (see picture) or traditional folded
  • Whether there is an additional filtration layer
  • In one recent review comparing 15 different designs and materials of cloth masks, the effective filtration rate varied from 28-90%, though 80% is frequently achieved

What is my summary  about cloth masks?

  • No cloth mask stops 100% of droplets 
  • There are inevitable uncertainties in the precise protection afforded by any individual mask 
  • Depending on the construction of the mask, an 80% reduction might be achieved but that might vary with the size of the droplets
  • The more an infected person shouts, coughs etc then the harder it is for a cloth mask to be effective
  • The longer the mask is worn the less effective it might be – but regular washing helps
  • The effectiveness of masks obviously depends on how they are worn, and whether they let out droplets round the side


  • Cloth masks are not the magic bullet to stop an infected person spreading the person, or protect an uninfected wearer from being at risk from others.  
  • Widespread usage might still have a major role in lowering the overall rate of infection in the population.  The size of this effect will be explored in my next post

Interested in further reading:

  1. How the effectiveness of different cloth masks can be measured.
  2. Study of the effectiveness of surgical mask against Covid-19. 
  3. A comprehensive  review of all the studies on the effectiveness of face masks.
Covid-19 Masks

Face masks: How much can they reduce the spread and duration of the epidemic?

There has been a continuing debate about the benefits from using face masks since the start of the epidemic.  The World Health Organisation was initially unconvinced of their benefit but recently changed its mind.  Socially and politically it has become the number one issue.  

Can enhanced wearing of face masks succeed where other means of managing the epidemic including  lockdowns, social distancing and track and trace have not?

This key question is surprisingly difficult to answer  but in this post I review what evidence is needed. 

Isn’t questioning  the benefits of face masks a no-brainer?

  • Covid-19 spreads from  an infected person by droplets,  with concentrations of virus particles increasing from normal breathing to shouting, sneezing  and coughing
  • Covid-19 spreads to a non-infected person either directly into their nose/mouth/eyes or indirectly by droplets picked up on the hands
  • Most spread is from people who are asymptomatic at the time they can pass on the infection.
  • Therefore people can reasonably say:
    • “If everyone around me wears a face mask, I am protected”
    • “If I wear a face mask, I am at least partly protected from others who may be infected” 

What’s the problem?

  • Not all face masks are effective at preventing spread
  • The way face masks are used may make them ineffective and possibly increase the risk of both causing and catching infection


  • Wearing a face mask for a long period of time is uncomfortable
  • As a society we rely for social interaction on seeing people’s faces – consider the issues raised by religious practice in this regard

And in addition:

  • Behavioural psychologists are concerned that by wearing face-masks, there is a relaxation of other protective behaviours such as social distancing.
  • It is reasonable to ask: “what is the additional value of wearing face masks if people adopt all other protective behaviours (distancing, hand washing etc)?”

The challenge from a research perspective in quantifying the benefits from face masks therefore comes from variability in:

  • Mask effectiveness
  • Safe mask use
  • Adherence to other protective behaviours
  • Background rate of infection in the population

Widespread wearing of face masks theoretically should  reduce risk to individuals, but in the real world it may not reduce the rate of infection in the population.

Is there a parallel with the vaccine question?

  • The current vaccines work and produce antibodies
  • But before being used we are having to await the results of experimental studies (clinical trials) where two otherwise equivalent groups of people are randomised either to active or inactive vaccine  to see over time how many become infected.  
  • We cannot do such a randomised study of face masks easily and thus have to rely on indirect evidence

The epidemiological train of thought!

  • Do current face masks do “what they say on the tin”, ie prevent transmission of viral particles:
    • This is not a yes/no question but the issue is more by how much is transmission reduced
    • How does this vary with type of mask?

There is no shortage of experimental data, eg direct measurement of the concentration of virus in air breathed or coughed out, to answer these questions

  • Assuming that these data confirm that most face masks in common use are a ‘sufficient’ barrier, there are two types of indirect information that can be looked at:
    • Ecological studies. These are studies comparing rates of infection between whole countries with different mask wearing behaviours.  Care is needed as a high mask wearing, low infection risk country might differ from other countries in other ways apart from mask use
    • Observational studies. The rates of infection are analysed in individuals who are believed to have similar exposures to the virus who are asked about their use of masks.  
  • Such studies may not capture the full range of current and future behaviours. These can be estimated from:
    • Modelling studies. As mentioned above there are so many factors that vary which will influence the impact of mask wearing on the rate of infection.  Different plausible scenarios can be compared by adjusting the level of, for example, of mask wearing and adherence to social distancing to estimate their combined  impact on the infection rate.  These simulations have emerged with some interesting insights on the relative value of masks


  • The data on the research referred to above will be summarised by me over the next week
  • I hope readers will not feel let down having read so far and not getting the full story in this post!
  • A complex question deserves not giving a simplistic answer
  • Spoiler alert – these data are reasonably  supportive of the additional benefit of mask wearing. 
Covid-19 Masks Vaccines

Corona Virus-(CoVid-19): what do we know?

[First circulated 25th February 2020]

What is the virus?

CoVid 19 is one of the family of viruses, the corona virus, that causes the common cold and is not, for example, part of the influenza virus group

How is it spread?

It seems that it is mainly spread from person to person and not via droplets hanging around in the air.  Although it can be spread direct into your nose, the hands can be a major source of infection: ie if you touch your face after your hands have had contact with the virus from an infected person

How infectious is it?

Experts probably don’t know exactly. There are two meanings of “how infectious”?

  • How many individuals can one person infect?  On average this appears to be quite small and a figure of 2-3 people get the infection from any one other affected person seems to be the major conclusion.  But this is  obviously influenced by how much contact such an individual has.  The idea of a ‘super infectious person’ is probably a myth
  • If you are not immune and you are sufficiently exposed to the virus, how likely is it you will get the infection?  Again, this is not clear, but seemingly the risk is  very high as few people will be naturally immune and the virus is quite effective

Are people infectious before they know they have the virus?

This appears to be the big problem and say differs from other corona viruses-if you have a cold you are only infectious when you have symptoms and are shedding the virus.  CoVid-19 has a particular property of fooling the body’s first line of immune defence when it enters the nasal airway.  The body’s first line defence is thus not activated and the virus multiplies and sheds.  So, for around 3 days after contracting the virus, the  infected individual, who will be feeling fine,  will be shedding virus into the air to those who are in close contact 

Are masks effective at preventing spread (should I wear one?)

Masks are now ubiquitous in China and other countries in South East Asia.   Obviously, carers and close family members of affected people should wear masks. There is now a world shortage of effective masks (most are made in China).  Indeed, the NHS is worried that there may not be enough for its own workers should a major epidemic take hold.  Experts say for low risk countries, such as the UK, it is unnecessary for normal healthy people to wear a mask to prevent them getting infected  All websites emphasise the importance of proper hand washing (with soap and water) and not touching the  face especially when having been in contact with a person with symptoms.

What are the consequences of getting an infection?

As the newspapers and other media report, the mortality rate is around 2% which is similar to that for normal seasonal flu.  Indeed, it might be lower than 2% as many mild cases are not reported.  But what about the other 98%. For most, the symptoms will be like a mild cold and chest infection. But, the problem is that the virus, not stopped by the body’s fist line of defence, then penetrates deep into the lungs and can cause pneumonia and other chest infections. This virus particularly likes the cells that line the lungs and sticks to them. The data from China suggest that perhaps 1 in 7 will have significant pneumonia.  Again, most such people will recover from a viral pneumonia.  There are a few people who then mount an exaggerated immune response to the infection in their lungs and then there is a massive battle between the virus and the immune response which can be very serious and probably explains the young deaths reported

Are any people specifically at risk of having a bad time?

As you might expect, elderly people, especially those over 80, with pre-existing lung disease and who have weakened immune systems are more likely to have complications and not be able to mount a good if delayed immune response.  But what about ‘normal healthy people?  The short answer is that the experts do not know why most previously healthy people have a mild disease while others  can get a significant pneumonia.  Interestingly, men seem to have worse disease (twice as likely to get complications – but this has been seen in other epidemics in the past eg SARS and MERS).  There may be a genetic risk, but what these are is not known

Why don’t some of the existing anti-viral drugs work?

Sadly, the drugs that were tested for treating other influenza outbreaks such as Relenza (Zanamivir)and Tamiflu (Oseltamivir) are  not likely to be effective against CoVid 19.  Indeed, despite government’s stockpiling millions of doses following the 2004 outbreak, the clinical trial evidence was even very weak for that and related epidemic.

An Israeli company has started an urgent clinical trial to see if they have an effective drug for the small number of people with acute severe pneumonia, but that is based on stopping the fight between the immune system and the virus and would not be used for ordinary infection 

Why can’t they get a vaccine quickly?

There is now a vaccine in trial against MERs, a related corona virus, which does seem to be safe and effective but will need to be tested on many more people.  The technology used to develop and test the CoVid-19 vaccine will be similar but honestly, it will be at least a year before large scale trials can begin I would imagine.  And remember, in a disease that for most people is very mild, if the vaccine has significant side effects in anything more than a tiny minority then its risks will outweigh its benefits

If people get infected are they then immune from further corona viruses

Again, not known, but based on SARS, probably some immunity but not life long