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Will covid-19 vaccines save lives? Current trials aren’t designed to tell us

BMJ 2020; 371 doi: (Published 21 October 2020) Cite this as: BMJ 2020;371:m4037

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Response to Gupta and colleagues

Dear Editor

Response to Gupta and colleagues

Thank you for your comments.

I would like to address your assertion that "if the mild illness due to any illness is prevented, the serious illness and deaths will also be prevented particularly at a population-level.”

First, I think it is reasonable to say that in a single human, preventing mild illness in that person should prevent that same person from experiencing further progression of the disease, thus preventing severe illness. (Of course there is no guarantee the person would progress to severe illness in the absence of vaccine, but the notion of nipping something in the bud is well taken.)

But it is a different matter to assume that a vaccine’s ability to preventing mild illness in one population (say, generally healthy, younger people) provides us with evidence of the vaccine’s ability to preventing severe illness in a different population (e.g. frail, elderly people). For example, influenza vaccine is well known to have lower efficacy in frail elderly compared to healthy adults. Nobody claims that an influenza vaccine that is 60% effective against lab-confirmed symptomatic influenza in healthy adults implies a 60% reduction against influenza deaths in the elderly.

My concern is as follows: the frail elderly are disproportionately contributing to the serious cases of Covid-19. Yet they were insufficiently recruited into the randomized trials. So we have precious little evidence from the trials on how effective the vaccines are in the very group that stands most to benefit from an effective vaccine.

This concern is not mine alone. The mistake of blindly extrapolating evidence from one population onto a different population for which we have ample reason to think vaccine response may be less robust was raised last October by a member of the U.S. FDA’s advisory committee.[1]

Peter Doshi


[1] FDA Vaccines and Related Biological Products Advisory Committee - 10/22/2020. Video: Transcript:

Competing interests: I am the author of the original article; please see that article for a declaration of competing interests.

08 April 2021
Peter Doshi
Senior editor
Baltimore, MD, USA