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expert reaction to JCVI announcement of second doses for 16 and 17 year olds, booster jabs extended to 40-49 year olds, and research from UKHSA on Pfizer booster effectiveness against symptomatic disease in the over 50s

Press releases from The UK Health Security Agency (UKHSA) announce the updated advice from The Joint Committee on Vaccination and Immunisation (JCVI) on COVID-19 boosters, and results from the UK real world study monitoring the effectiveness of COVID-19 booster vaccination.


Professor Lawrence Young, Virologist and Professor of Molecular Oncology, University of Warwick, said

“Both the UKHSA study and data from Israel where the booster programme was rolled out to anyone over the age of 12 in August highlight the effectiveness of booster jabs in protecting from symptomatic disease. Boosters will also significantly limit virus transmission and this is reflected in the massive reduction of cases observed Israel – from a 7 day average of almost 11000 cases on 14th September to 457 cases on the 14th November. It’s likely that more widespread rollout of booster jabs to younger age groups will be needed to provide a higher level and longer duration of protection that will drive down transmission in the community. It also likely that we also need to further extend the vaccination programme to give 12 to 15 year olds a second jab and to consider vaccinating 5 to 11 year olds as has already started in the US and is about to start in Israel. Altogether this will reduce the overall community spread of coronavirus, prevent the generation of new variants, protect the NHS from being overwhelmed over the winter and, hopefully, force the virus into a more manageable endemic infection.”


Dr Peter English, Retired Consultant in Communicable Disease Control, Former Editor of Vaccines in Practice, Immediate past Chair of the BMA Public Health Medicine Committee, said:

“You reach herd immunity when fewer than one of the people you would have infected is still susceptible to infection. This means that they are unable to be infected. (NB – to be infected and infectious, not to be symptomatic. What really matters is the proportion of the secondary cases who will, in turn, be infectious and able to generate tertiary cases.)

“R0 (subscript zero) is a theoretical measure of how infectious a disease is. It is the number of people which (on average) each case will infect. It is pronounced “R-nought” (or, if you’re American, “R-naught”.)

“Of course “on average” is doing a lot of heavy lifting here. Some people have a lot more contacts than others. Children and teenagers tend to have very high numbers of contacts; retired people probably relatively few (on average). And people who have more contacts will infect more people… 

“It’s also the case that the number of people each person infects is far more variable for Covid-19 than it is for other diseases, such as flu…

“For the delta variant of SARS-CoV-2 virus, R0 is thought to be somewhere between 5 and 10. 

“But if we keep it simple, let’s pretend everybody is equally likely to be infected/infectious. And for the ease of the arithmetic, let’s pretend Covid’s R0 is 10…

“That being the case, to achieve herd immunity, you’d have to get immunity rates >90%. That way, more than 9 of the people 10 people you would otherwise have infected will be immune, unable to be infected. If the disease has an R0 of 5, then you’d need to ensure >4 out of every five people are immune – an immunity rate of >80%. 

“Of course, it’s more complicated than that. What’s the R value for people who have had one, two or three doses – how many people will they (on average) go on to infect? It’s likely that people will be less likely to be infected/infectious… And it’s more important, if your goal is herd immunity, to get the people who have the most contacts with other people immune, unable to be infected and infect others…

I have estimated that, after two doses of vaccine, the chance of having any infection is likely to be about 30% what it would if unvaccinated – so the maximum proportion of the population you could get immune and unable to pass the disease on is about 70%. If R0 is as high as 5 – let alone as high as 9 or 10 – you will never achieve herd immunity, even if 100% of the population is vaccinated.

“The UKHSA study does not give us any information about the proportion of people who are infected and able to be infectious – just about the proportion who get symptomatic disease after three doses, compared to people who are unvaccinated, or who have received only two doses.

“In order to know how much effect this will have on disease transmission, you need to know what proportion do not become infectious – which means detecting any infection, or observing a decrease in transmission… Such studies are much harder to do, and/or take much longer.

“But after three doses – based on the Bar-On et al. paper – I estimated that only about 3% of the population can be infected. If you gave everybody three doses of the vaccine, you’d have 97% immunity – more than enough for herd immunity, even if R0 is 10.

“On this basis, it seems unlikely that we will achieve herd immunity with a two-dose vaccination regime, but if we can get enough people vaccinated with three doses – and especially, enough of the people who have a lot of contact with others people – we would be able to achieve population immunity. 

“(I have been predicting, confidently, for some time, that the vaccines will become a three-dose vaccination programme, like so many of our other vaccine programmes: a three doses “primary course”; which may subsequently be followed a year or more later by a reinforcing dose, if immunity wanes, or if vaccine-escape variants arise.)

“But – especially since children and young people tend to have a lot of contacts – we don’t have a chance of achieving herd immunity with vaccination alone, unless we can get a large proportion of children and young people fully (three-doses) vaccinated.”


Prof Penny Ward, Independent Pharmaceutical Physician, Visiting Professor in Pharmaceutical Medicine at King’s College London, said:

“JCVI have sensibly updated guidance on COVID boosters and extended eligibility for these to a younger population following evidence of waning effect in in this age group who are now approaching the 6 month mark post completion of their initial course. There is a possibility that we will see further extensions of the booster campaign to younger age groups still as time progresses given that response to the initial vaccination course generally wanes over time, even among younger people, albeit at a faster rate in those of more advanced years who are also at risk of more severe disease. The UKHSA data, published today, provides a rapid evaluation of protection against symptomatic disease following receipt of a booster shot, indicating prompt reduction in risk from as early as 7 days post injection, with greater protection still anticipated against severe disease/death – although too soon to be observed in the data at this point. This information should encourage individuals to present for their booster vaccinations to protect themselves from illness.

“In addition today has come the welcome news that the risk of post vaccine myocarditis in the UK is low, providing confidence to the JCVI and enabling them to recommend the second vaccination for 16-17 year olds. This group have been at the greatest risk of infection during the autumn, and the second shot will provide them with greater protection as the winter approaches.

“As the daily infection rate starts to go up again, high time that we all come forward to take our offered boosters – increasing the number of people with high level immunity might yet save Christmas!”


Prof Paul Hunter, Professor in Medicine, The Norwich School of Medicine, University of East Anglia, said:

“This is the first real evidence of the effectiveness of the booster in the UK setting. It confirms what has been reported from Israel about the impressive effectiveness of the booster dose. This is perhaps even more impressive when considering that a significant proportion of people who have not yet had their booster will have had an infection and so had some additional protection now. This report also gives reassurance that whether someone had AZ or Pfizer as their first course, the booster provides similar excellent protection.

“It is too early to know how effective the booster will be in the UK to at reducing the risk of hospitalisation. But from the Israeli experience we can expect the booster to be even more effective at preventing severe disease than at preventing symptomatic infection.”


Dr Simon Williams, Senior Lecturer in People and Organisation, Swansea University, said:

“Today’s decision to extend booster jabs to all adults over 40 and to offer second jabs to those aged 16-17 are important developments in the fight against COVID-19 this winter.

“Research suggests that intentions to get a booster vaccine are really high, and so we can expect that uptake will be high. For example a recent survey1 found that 8 out of 10 adults who had received two doses would get a booster if offered.  Our research2 is finding that for many people the reasons behind getting a booster were the same as the reasons behind getting the initial vaccine, to protect others as well as themselves; for many the booster is a seen as an inevitable extension of the immunity the initial vaccine offers.

“However, some real challenges remain.  Firstly, it is important to ensure that intentions are followed by action.  In psychology, there is something called the intention-action gap, which is where some people have good intentions, but don’t necessarily ‘follow-through’ with action. There is a worry that this might happen a bit with boosters – certainly many people perceive covid as less of a threat now than they did last winter when the initial vaccines were starting to be rolled out, and less perceived threat means some may be less inclined to take up the offer of a booster as quickly as they did first time around.

“Also, it is not just about getting the ‘arms to the jabs’ but also about getting the jabs to the arms.  There are concerns that the boosters are not being rolled out quickly enough3 to the high priority groups, and so unless things speed up in the coming weeks, the gap between the number who have had the booster and the total number are eligible for it – currently about 6 million4 –  is likely to remain or even widen.

“We need to get booster opportunities out into communities, scaling up mobile vaccination sites, vaccinating with the same kind of urgency we did at the start of 2021.  Also we need to continue to address the disparities in vaccinations amongst certain groups, for example ethnic minority groups, as shown in today’s ONS figures5. If we don’t hit high booster uptake, coupled with other protective measures like mask wearing, good ventilation, Covid passes and support and encouragement for proper testing and self-isolation, then many preventable deaths will occur and there is a real risk NHS capacity will be stretched to bursting this winter.

“It is also encouraging to see the second vaccination being offered to 16-17 year olds.  We know how crucial the second jab is to reducing the risk of transmission to close others.  And so with many young people understandably wanting to see their grandparents or other potentially higher-risk people over Christmas, a quick and effective roll out to these groups will definitely help contribute to a safer Christmas (along with all the other basics about minimising indoor contacts, wearing masks where appropriate and ensuring adequate ventilation by opening the windows at least once per hour for ten minutes.”


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Prof Sir David Spiegelhalter, Chair, Winton Centre for Risk and Evidence Communication, University of Cambridge, said:

“These are very encouraging results. The booster appears to give similar protection against symptomatic disease as that obtained soon after two Pfizer doses, whatever the initial vaccine. This means those who initially had AstraZeneca will have more protection than they ever had.

“An earlier study from this team estimated that double-Pfizer jabs gave around 99.7% protection against hospitalisation, but which waned to 92.7% after 20 weeks. This may not sound much, but, in terms of ‘lack of protection’, it means their vulnerability relative to being unvaccinated went from 0.3% to 7.3%, more than a 20-fold increase in risk, which gives a stronger impression of the importance of waning immunity. Fortunately, the latest data suggest the booster may rectify this.”


Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, said:

“Administering a third dose shows a very strong immune response, and the emerging UK data shows that there is 93% protection against symptomatic infection. Protection against severe COVID-19 illness will be even higher than that. Similar findings are coming from other countries that have an advanced booster programme, such as Israel. This is an excellent outcome and indicates that the advice to offer booster doses to the over 40s is a good move. A winter of COVID-19 and flu brings huge uncertainty around the potential impact on those infections upon the health service, so the more immunity we can build up now, the better.

“Given the waning of immunity around 6 months after initial immunisation, it may be that the longer-term outcome is to regard COVID-19 vaccination as a three-dose schedules, rather than 2 doses and a booster when necessary. There are other example of three-dose immunisations. In the UK, these include the meningitis B vaccine, and also the ‘6 in 1’ vaccine.”

UK schedule –


Dr Thomas House, Professor of Mathematical Sciences at the University of Manchester, said:

“The decisions to recommend extension of the UK’s vaccination programme make sense, both from the point of view of individual safety, and from the point of view of helping to reduce the overall burden of COVID in society over the coming months. This is likely to be particularly important as the usual Winter pressures on the healthcare system are expected to be worse than usual due to resurgent endemic disease and a backlog of other conditions. Throughout the pandemic, JCVI has taken a measured approach to vaccination roll-out, and I believe that the public should have confidence in their decisions. Although there is a lot of room for legitimate scientific debate on the exact timings and groups involved, decisions are being made in a way that is clearly intended to maximise long-term trust in the safety and efficacy of the UK’s vaccination programmes. The main concern I think that should be raised with the UK’s vaccine strategy is the international angle. Pandemics demonstrate more than anything that the relevant division is “humanity versus the virus”, and the failure to provide adequate vaccine supply to the poorer countries that need it is shameful from the point of view of basic justice. Even from a ‘selfish’ point of view, the emergence of the Delta variant shows how uncontrolled transmission in one area of the World can cause major problems elsewhere. We need urgent consideration of how to ensure equitable access to vaccines throughout the world.”



JCVI issues advice on COVID-19 booster vaccines for those aged 40-49 and second doses for 16-17 year olds –

Study press release – Boosters give over 90% protection against symptomatic COVID-19 in adults over 50

Study – Effectiveness of BNT162b2 (Comirnaty, Pfizer-BioNTech) COVID-19 booster vaccine against COVID-19 related symptoms in England: test negative case-control study –



All our previous output on this subject can be seen at this weblink:



Declared interests

Dr Peter English: “Dr English is on the editorial board of Vaccines Today: an unpaid, voluntary, position. While he is also a member of the BMA’s Public Health Medicine Committee, this comment is made in a personal capacity. Dr English sometimes receives honoraria for acting as a consultant to various vaccine manufacturers, most recently to Seqirus.”

Prof Penny Ward: “I am semi-retired, but I am owner/Director of PWG Consulting (Biopharma) Ltd a consulting firm advising companies on drug and device development. Between December 2016 and July 2019 I served as Chief Medical Officer of Virion Biotherapeutics Ltd, a company developing antiviral treatments for respiratory viral diseases. Previous employee of Roche, makers of tocilizumab (anti IL6 antibody) and CMO of Novimmune, makers of empalumab (anti IFN gamma antibody).”

Prof Sir David Spiegelhalter: “I am a Non-Executive Director of the UK Statistics Authority, which oversees the work of the Office for National Statistics.”

None others received.

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