Faced with the limited number of doses available, the British decided to postpone the second injection planned for the Pfizer-BioNTech vaccine. This decision could have an impact on its effectiveness.

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Can we delay the second injection of Pfizer-BioNTech vaccine?

  • Why did the British take such a decision?

They are currently facing a health crisis much more serious than last spring because of the new variant of the virus. This would indeed be much more contagious. The British therefore took emergency measures and in particular the postponement of the second dose of vaccine.

  • Does the first injection effectively protect patients?

In theory, according to the marketing authorization, the effectiveness of this vaccine is based on performing a first injection followed, 21 days later, by a second. It is only after this protocol that 95% protection is obtained, even with 3 months of follow-up according to the data published in the New England Journal of Medicine. However, the authors also provide information on the monitoring of patients between the two doses. From the 12th day after the first injection, the effectiveness would be at least 52%.

  • 52% effectiveness after a single dose: is it enough?

This is not ideal, of course, as Professor Chris Whitty, responsible for the equivalent of our scientific council, explained to his fellow citizens yesterday. But, as the number of doses available today is too small, it is better to protect twice as many people faster. The British Society of Immunology has given the green light. This considers that “Postponing the second dose should not have a negative effect on the final immune response”. In other words, we would ultimately achieve 95% protection. But, on condition of not exceeding 12 weeks.

  • Has this strategy been validated by the World Health Organization?

Yesterday, the WHO admitted the possibility of this postponement in exceptional circumstances. In the event of an extremely serious epidemic, this option can make it possible to maximize the number of people who would benefit from protection. Today, France does not feel concerned. It therefore follows the conditions of the marketing authorization. But, that could change if the new English strain spreads more strongly in our territory.

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