Intended for healthcare professionals


Delaying the second dose of covid-19 vaccines

BMJ 2021; 372 doi: (Published 18 March 2021) Cite this as: BMJ 2021;372:n710

Read our latest coverage of the coronavirus outbreak

  1. Dominic Pimenta, chair1,
  2. Christian Yates, senior lecturer2,
  3. Christina Pagel, professor of operational research3,
  4. Deepti Gurdasani, senior lecturer4
  1. 1Healthcare Workers’ Foundation, London, UK
  2. 2Department of Mathematical Sciences, University of Bath, Bath, UK
  3. 3University College London, London, UK
  4. 4William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, London, UK
  1. Correspondence to: D Pimenta dom{at}

Concerns remain about effectiveness in older adults

On 30 December 2020, the UK announced a deviation from the recommended protocol for the Pfizer-BioNTech covid-19 vaccine, prolonging the interval between doses from 3 to 12 weeks.12 Similar decisions were made for the Oxford-AstraZeneca vaccine, for which a longer gap between doses had been shown to improve efficacy in some age groups.3

The stated intention was to maximise benefit with limited supplies and to minimise hospital admissions and deaths. For the Pfizer-BioNTech vaccine, the decision to delay the second dose was based on extrapolations from phase III trial data showing an efficacy of 89% 15-21 days after the first dose.45At the time, Pfizer did not support the decision, stating that high efficacy could not be guaranteed.6

Efficacy in elderly people seems excellent after two doses of the Pfizer-BioNTech vaccine.7 A longer gap between doses may improve the long term immune response, as seen with AstraZeneca’s vaccine.38 However, as many people in priority subgroups have not yet received a second dose, any substantial waning of protection during the 12 week …

View Full Text