The primary aim of all vaccination campaigns is to stop people getting seriously ill and save lives.  However, no vaccine is 100% effective in stopping disease and so it’s important that we monitor vaccine rollout and examine any cases where an individual is hospitalised for COVID-19 following vaccination.  This will help us refine and improve vaccination regimes in future.

This SAGE report using ISARIC4C and CO-CIN data is not peer-reviewed research but rather a description of trends observed in the initial months after COVID vaccine rollout in the UK.  The most important point to make is that we know from other studies that all COVID vaccines available in the UK are highly effective in preventing serious disease and hospitalisation from COVID-19.  This paper examines the very small minority of people for whom this is not the case.

The immune response generated by any vaccine takes a minimum of 10-14 days to develop the all-important immune memory that stops us getting sick if we come in contact with the real virus.  We would not expect any vaccine to have much, if any, effect on disease hospitalisation rates before 14 days post-vaccination, as the immune system is still building its memory and protection will not yet be up to maximum power.  According to this paper, the majority of hospitalisations for COVID-19 post-vaccination take place in this 1-14 day window when protection from the vaccine is not yet fully active.  This shows the importance of maintaining social distancing, even after vaccination, to minimise the risk of contracting SARS-CoV-2 before your immune protection is active.

A very small number of people were hospitalised 21 days post-vaccination and it’s these people that we need to examine in more detail to understand why the vaccine did not afford them full protection.  Understanding what immunologists call the ‘correlates of protection’, or what effective immunity against COVID-19 looks like at the cellular level, will help provide answers to this.

Overall, we can be confident that the COVID-19 vaccination programme is highly effective in preventing serious disease and saving lives.  I urge anyone who is offered a COVID vaccine to get it.  However, let’s not be complacent and let’s continue monitoring the vaccine rollout to refine our response and make sure we continue to hasten the end of the pandemic.

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This paper reports on data collected by the Coronavirus Clinical Characterisation Consortium.  The paper was not designed to test a hypothesis but, rather, describes data, from which hypotheses could be generated.

It tells us the proportion of patients admitted to hospital who had been vaccinated, with considerable detail about e.g. the interval between vaccination, the onset of symptoms, and hospital admission.

The proportion of patients admitted who had been vaccinated will depend on a number of factors, not least the proportion of the background population who have been vaccinated.  It will also depend on how effective the vaccines are.  Other trials and surveillance data show that vaccines are less than 100% effective, at preventing serious illness, so of course some vaccinated people will continue to become ill enough to require hospital admission.

Vaccines take time to provide immunity.  In the first week after vaccination they have little effect, but vaccine efficacy rises rapidly over weeks two and three, and then the increase slows down; but it doesn’t completely plateau until week four, five, or later.  As a result, many people who get ill with Covid-19 after vaccination do so before you would expect the vaccines to have had their full effect.  This paper describes the proportions of people admitted who have been vaccinated at different intervals, and find that many are admitted before the vaccine has time to generate protective immunity.

There is a possibility that the rate of disease increases just after vaccination: the paper discusses why this may be and suggests in some cases people might have been infected when attending for vaccination, or as a result of behaviour changes based on the false idea that they are already protected, days after vaccination.  The authors also suggest that some of these people might be admitted to hospital because of a reaction to the vaccine rather than because of COVID-19: many vaccine recipients have a fever shortly after vaccination, although it usually subsides within 48 hours.

The paper confirms that the vaccine is not 100% effective; and that people who do acquire the infection despite having been vaccinated and become ill enough to require hospital admission do not seem to have a reduced risk of death.  This would suggest that if vaccines fail to prevent the immune over-reaction that is associated with hospital admission, they have no further effect.  This is not a surprising conclusion.  Once the immune over-reaction phase of the illness starts (and it is usually this that causes illness severe enough to require hospital admission, the presence of the virus is no longer a factor in the subsequent course of the illness.  At this point, treatments that attack the (now non-existent) virus are of little or no value.  We have seen this with antivirals and monoclonal antibodies, so it would be surprising if natural (disease or vaccine-induced) antibodies were any more effective.

There are no real implications from these data, other than that they are consistent with what we would expect given what we already believed we knew about the response to vaccines at a population level.

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