Effectiveness of the COVID-19 vaccine after first use: Pfizer, Moderna, AstraZeneca


In a letter to the editor published in the New England Journal of Medicine, Dr. Danuta M. Skowronski and Dr. Gaston De Serres used the dossier submitted to the Food and Drug Administration to infer vaccine efficacy for Pfizer’s COVID-19 vaccine, BNT162b2.1 in the original study published by Polack et al. The efficacy after the first dose was calculated to be 52.4% and it was collected in the first 2 weeks after the injection when “the immunity would have increased”. 1.2

Their analysis concludes that BNT162b2 was 92.6% effective before the second dose.

Dr. Skowronski and Dr. De Serres further recommend: “With such a highly protective first dose, the benefits of a scarce vaccine supply could be maximized by postponing the second dose until all members of the priority group are offered at least one dose.”

There are limited data on an alternative vaccination schedule and duration of protection after the first dose. Corresponding authors, however, indicate that following the current vaccination schedule is of little short-term benefit given the current vaccine shortage.

Pfizer’s response to the authors underscores the lack of data on alternative dosage regimens. “The decision to introduce alternative dosage regimens rests with the health authors,” the report said. Pfizer representatives reiterate the importance of monitoring the alternative dosage schedules implemented to ensure that vaccines provide the best possible protection.


The first-dose efficacy analysis of Pfizer is similar to Moderna COVID-19 vaccine mRNA-1273, which was reported to be 92.1% in an FDA briefing document published December 17, 2020


The results of three single blind randomized controlled trials in the UK, Brazil and South Africa indicated that a 3 month dose interval could have advantages over a short dose interval.4 This change serves two purposes: to vaccinate the largest population when supplies are scarce and to protect after the second dose should be improved.

An exploratory analysis showed that the vaccine effectiveness against primary symptomatic COVID-19 was 55.1% (95% CI, 33.0-69.9%) at an interval of less than 6 weeks and 81.3% (95%) CI, 60.3-91.2%) at an interval of at least 12 weeks.

Efficacy against asymptomatic infections in the UK showed similar results, with increased efficacy correlating with longer intervals.

A single standard dose of the vaccine has been shown to maintain 76% (95% CI, 59.3-85.9%) effectiveness against primary symptomatic COVID-19 for the first 3 months after vaccination. However, it does not protect against asymptomatic infections over the same period (vaccine effectiveness -17.2%; 95% CI -248.6 to 60.6%). A single dose demonstrated protection against any nucleic acid amplification test positive infection from 22 to 90 days.

“Immunization programs that aim to vaccinate a large portion of the population with a single dose, with a second dose given after a period of three months, could be an effective strategy for reducing disease,” the study’s authors concluded.


1. Skowronski DM, De Serres G. Safety and effectiveness of the BNT162b2 mRNA Covid-19 vaccine. Letter. N Engl J Med. Published online February 17, 2021. doi: 10.1056 / NEJMc2036242

2. Polack FP, Thomas SJ, Kitchin N. et al .; for the clinical trial group C4591001. Safety and efficacy of the BNT162b2 mRNA COVID-19 vaccine. N Engl J Med. Published online December 31, 2020. doi: 10.1056 / NEJMoa2034577

3. Advisory Committee on Vaccines and Related Biological Products FDA Briefing Document Meeting: Moderna COVID-19 Vaccine. December 17, 2020. Accessed February 23, 2021.

4. Voysey M., Clemens SAC, Madhi SA, et al .; on behalf of the Oxford COVID Vaccine Trial Group. Single-dose administration and the effect of booster dose timing on immunogenicity and efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine: a pooled analysis of four randomized trials. Lancet. Published online February 19, 2021. doi: 10.1016 / S0140-6736 (21) 00432-3

This article originally appeared on Infectious Disease Advisor

Related Articles