Intended for healthcare professionals

Letters Vaccine interval policy

Optimal dosing interval for covid-19 vaccines: we need clinical trial evidence and to consider past infection

BMJ 2021; 372 doi: (Published 24 February 2021) Cite this as: BMJ 2021;372:n522
  1. Ulrich Müller-Sedgwick, consultant psychiatrist1 2
  1. 1Barnet, Enfield, and Haringey Mental Health NHS Trust, London N15 3TH, UK
  2. 2Department of Psychiatry, University of Cambridge, Cambridge, UK
  1. um207{at}

I agree with Chatterjee that “the decision to delay the second dose of the Pfizer vaccine against covid-19 has caused significant disquiet among healthcare workers in the UK.”12 I wonder why two obvious solutions have not been discussed in the medical literature and media.

Firstly, we don’t know which dosing interval of three (Pfizer BioNTech), six (World Health Organization), or 12 weeks (UK government) between the first and second dose of the Pfizer vaccine gives more efficient protection from infection.34 This is a case for an urgent pragmatic clinical trial comparing those dosing intervals. Most NHS clinicians would sign up for such a trial, as there may be different benefits from the shorter (better protection in the first weeks) and longer dosing intervals (longer lasting protection).

Secondly, people with a previous coronavirus infection (among them many NHS clinicians and other public facing workers)2 will have some degree of natural immunity. We don’t know how long this lasts after different clinical and non-symptomatic presentations of covid-19.5 For this group the first vaccine dose works like the second booster dose in people without a previous infection. A possible compromise in the current scenario of high infection rates, high risks for frontline workers, and limited vaccine availability would be to postpone the second dose of the Pfizer vaccine only in healthcare workers who had a documented infection in the past year or six months.


  • Competing interests: I had the first dose of the Pfizer vaccine more than three weeks ago.

This article is made freely available for use in accordance with BMJ's website terms and conditions for the duration of the covid-19 pandemic or until otherwise determined by BMJ. You may use, download and print the article for any lawful, non-commercial purpose (including text and data mining) provided that all copyright notices and trade marks are retained.


View Abstract