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expert reaction to abstract on protection against COVID-19 from a booster dose of Pfizer looking at data from Israel

An abstract, published in the New England Journal of Medicine (NEJM), looked at protection against COVID-19 from a booster dose of Pfizer using data from Israel.


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:

“This comment is based on a pre-print, as the final NEJM paper is not (at the time of writing – about 17:30 UK time on 15 Sept) yet available.1 The pre-print, however, has a very similar abstract.

“This is excellent news about the effectiveness of a booster dose.

“In this comment I shall set aside the questions of global equity and whether or not it is better to use available vaccines in this way in the UK, or to send them to lower income countries in which many people are as-yet unable to be vaccinated.

“You may find this twitter thread helpful if you want to go into more details of the study.2

“The study was undertaken in Israel, which was one of the first countries to vaccinate a high proportion of its population, using the BNT162b2 messenger RNA vaccine (Pfizer–BioNTech), with a three-week interval between doses (the primary course of vaccination). This study looks at the effectiveness of a booster dose given to people aged 60 years or more, at least 5 months after the primary course. This was a large, population-based study, looking at well over a million people, with sound methodology, so the findings are likely to be robust.

“Note that the figures quoted compare the effectiveness of vaccination in the group who had received the booster dose, to the effectiveness in people who had received a full primary course of vaccine. They thus refer to the effectiveness of the booster dose over and above the routine two-dose primary course.

“The study found that, from 12 days after the booster dose, the rate of confirmed infection was about a tenth (11.9%) in the booster dose group than it was in the non-booster group; and the rate of severe illness was about a fifth (19.5%). (The paper also looked at vaccine effectiveness less than 12 days after giving the booster dose. It is not clear why. Vaccine efficacy rises very quickly after giving a booster dose – the primed immune system kicks in very quickly. But it is not instant; and in population terms, we would not expect the full effect to arise until a few days, maybe as long as 12 days after vaccination, so their finding that effectiveness was lower before this point is only to be expected.)

“Remember that vaccination is most effective against severe disease (causing hospitalisation, ICU admission, and/or death); less effective against less severe symptomatic disease, and less effective again against asymptomatic infection (which is important because people with asymptomatic infection may be infectious, and are less likely to take precautions to infect others, because they are unlikely to know they’re infectious).

“As background, the latest PHE report suggests that two doses of vaccine against serious disease is symptomatic disease and against any infection (including asymptomatic) is 65 to 90%; and against hospitalisation it is >94%. In round figures, that would suggest that the rates of any infection in vaccinated people are about a fifth what they are in unvaccinated people; and the rates of severe illness are about a 20th. The report also suggests that those individuals who are infected despite being fully vaccinated were up to half as likely to infect others.3 4 (We know that people who have so-called “breakthrough” infections may have as much virus in their respiratory secretions as unvaccinated people; but it is likely that the duration of infectiousness will be considerably less.)

“This being the case, if this paper’s findings apply equally in the UK population (and there’s no reason to think they won’t), the risk of people who receive a booster dose being infected (and thus able to infect others) might be expected to drop from about a fifth, to a fiftieth what they are in unvaccinated individuals; and the rates of severe infection drop to about 1% of what they are in unvaccinated individuals.

“These are spectacularly good results, which are likely to have a very significant effect on the direct risk to individuals who receive a booster dose, and also to the risk of their becoming infected and transmitting the disease to others; and thus on transmission rates and the effective R number.

“It is unclear whether such improvements will be seen in the UK. Here, we mostly used a longer prime-boost interval than was used in Israel, which enhanced the initial vaccination effectiveness, so we might not see quite as big an improvement as they found in Israel. But even if the effect of giving a booster dose of vaccine is not as good as this paper found it to be in Israel, they could be extremely beneficial here in the UK.”


  1. Bar-On YM, Goldberg Y, Mandel M, Bodenheimer O, Freedman L, Kalkstein N, et al. BNT162b2 vaccine booster dose protection: A nationwide study from Israel. medRxiv 2021:2021.08.27.21262679. (
  2. Amir O. @ofraam: A new pre-print from a group of researchers in Israel shows very high efficacy of a booster dose TLDR – the booster seems to be working great! (thread). Twitter thread 2021; Updated 29 Aug 2021; Accessed: 2021 (12 Sep): ( or
  3. Public Health England. COVID-19 vaccine surveillance report: 12 August 2021: Week 36. COVID-19 vaccine surveillance reports 2021; Updated 09 Sep 2021; Accessed: 2021 (10 Sep): ( or via
  4. Public Health England. COVID-19 vaccine surveillance report: 1 July 2021 (week 26). COVID-19 vaccine surveillance reports 2021; Updated 01 Jul 2021; Accessed: 2021 (01 Jul): ( or via



Protection of BNT162b2 Vaccine Booster against Covid-19 in Israel’ by Yinon M Bar-On et al. was published in the NEJM at 22:00 UK time on Wednesday 15 September.


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.

None others received.

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