Will vaccines protect against Omicron: what, when and how we will know?

The big question worldwide is ‘will current vaccines be effective against Omicron?’  In the absence of any real hard information, news media are reporting on every expert utterance and each new case.  In this post I will try and provide a foundation for how to interpret the emerging information.  

Let us be clear on the important questions!

Given where we were a week ago (what a long time ago that seems!) this is what we knew – that:

  • Delta variant predominated
  • Delta is highly transmissible and responsible for the recent surge in Europe
  • Vaccines reduced Delta transmission by a reasonable amount but the likelihood of severe infection by a very substantial amount
  • These vaccine successes were enhanced in those who had had a third dose

To me, the important questions about Omicron are therefore:

  • Is Omicron more transmissible than Delta in individuals who have been vaccinated – and if so, by how much?
  • Is infection with Omicron more severe than with Delta in individuals who have been vaccinated – and if so, by how much?
  • For each of the above questions, we would want the answers broken down by:
    • Which vaccine
    • One, two or three doses

What do we have at the moment: expert opinion

  • In the absence of any real evidence, media are seeking out expert opinion
  • In fairness, the opinions are not based on just hunches but based on scientific assessment, in this case, of the relationship between the mutations described and what we know about the virus and the body’s immune response to the current vaccines 
  • The problem is experts’ opinion is just that, and given all the uncertainties, they won’t agree: for example this is the bosses of the 2 mRNA vaccines who said different things yesterday!
  • (I know from my own experience with the media on complex issues such as this, you won’t get quoted unless you come off the fence!)

What do we have at the moment: anecdotes

  • Epidemiologists use the term ‘anecdote’ to cover for example information that comes from just one or maybe a group of patients, but without any statistical underpinning
  • We cannot know what these limited reports mean in terms of our big questions
  • Under this category for example would be these recent reports about Omicron that there were 
    • “9 cases of infection from a single source in Scotland” 
    • “Some cases in South Africa have had 3 doses of the vaccine”  
    • “Most cases in Southern Africa have been mild or asymptomatic”  
    • “No cases of severe infection have been reported amongst the 44 known cases (to yesterday) in Europe”

  • Undoubtedly there will be a case soon in Europe of a triply vaccinated person who becomes hospitalised because of Omicron, and this will be headlines around the world
  • As an epidemiologist, I find both these ‘worrying’ and ‘reassuring’ stories to be of some interest, but they do not and cannot answer my key questions above

What we will get soon: lab studies

  • Laboratories are working round the clock testing the response to Omicron in people who have been vaccinated
  • The results should come in about 2 weeks
  • We should expect, because of the complexity of the experiments, that not all labs will produce the same results!
  • Below I show in simple terms one of the main approaches
  1. Scientists produce a virus which is harmless but is ‘engineered’ to have the same spike mutations

2. They will then take blood samples from people who have been vaccinated with different doses or none, and mix the new Omicron lookalike virus with these blood samples.

3. They will then measure how much response there is in terms of both antibodies and T cells, and if they are strong enough to fight the infection

  • Whilst these results will be very useful, especially if they show that, say after 3 doses of vaccine, the cells produce enough antibodies and T cells to combat the virus 
  • The problem is that what happens in the test tube does not necessarily correspond to what happens in real life

What we will get: real world epidemiological data

  • The proof of the pudding in terms of my key questions above will come from collecting real data from patients
  • Many countries including Israel, UK and Netherlands can link individuals’ vaccine details with national data that provide subsequent rates of (i) any infection (from the national testing) and (ii) being admitted to hospital with Covid-19    
  • Epidemiologists will need to examine these data on rates of infection, relative to how many doses of vaccine, and compare these results between infections from Delta and from Omicron
  • The data will only be useful when enough cases have emerged from Omicron in the different vaccine groups
  • Paradoxically if there are very few triply vaccinated individuals who become hospitalised in the next few weeks, especially as Omicron may take time to become (if that is the likely outcome) the predominant strain, we might take reassurance from the low numbers but they won’t be able to provide a robust statistical answer to my questions 


  • Scientists have set this Omicron ‘hare’ running and for very good reasons
  • If the resultant publicity then leads to greater uptake of boosters and mask wearing, then all to the good for managing the consequences of infection with Delta
  • Just be cautious in how you interpret all the material that is emerging on a daily basis!

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4 replies on “Will vaccines protect against Omicron: what, when and how we will know?”

This mask-wearing thing: I use disposables, usually for a few minutes as I shop really fast and rarely use public transport. So I tend to stick them on my sleeve and re-use. Obviously they’re supposed to be single use. But apart from the ocean of waste generated it pains me to throw them away until I’ve used them 3 times. And when I say 3 times I probably mean about 33. Are they really only good for single use? What’s the half life of a disposable mask?


Your measured scientific comments are always very helpful in understanding the constantly developing virus, thank you.


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