Study results published in The Lancet showed that a single dose of Pfizer and BioNTech’s COVID-19 vaccine BNT162b2 is 85% effective at preventing symptomatic disease 15 to 28 days after being administered. The data, which come from an analysis of healthcare workers in Israel, also indicated that a single dose of the vaccine is 75% effective at preventing all SARS-CoV-2 infections, which includes both symptomatic and asymptomatic cases.
“This is the first study assessing effectiveness of a single vaccine dose in real-life conditions and shows early effectiveness, even before the second dose was administered,” remarked study author Eyal Leshem. The data were collected from 9109 healthcare employees at the Sheba Medical Centre, which began its vaccination program on December 19.
In the final results from Pfizer and BioNTech’s phase 3 study, BNT162b2 had an efficacy rate of 95% 1 week after the second dose, with recent data from real-world use in Israel showing that the mRNA-based COVID-19 vaccine cut the number of symptomatic COVID-19 infections by 94%. Meanwhile in the original late-stage trial, BNT162b2 demonstrated effectiveness of 52.4% after one dose, although it did not differentiate between before and after two weeks.
Commenting on the Sheba Medical Centre analysis, study author Gili Regev-Yochay noted that the results may differ from others because the subjects were largely younger and healthier as “we don’t have many (staff) here aged over 65.” She added that the analysis also could not confirm how long protection from one dose would last, as 66% of the healthcare workers had been given their second dose by January 24, with 91% of these receiving it on days 21 or 22.
Data back delaying second dose
However, in an appendix to the latest study, results showed that the effectiveness of BNT162b2 in preventing symptomatic COVID-19 was 94% at 22 to 28 days after the first dose. That accords with an estimate cited in a recent NEJM letter, in which two researchers said their analysis of Pfizer data submitted to the FDA indicates the vaccine is 92.6% effective in the 2-week period after the first dose and before the second. Findings such as these have prompted calls for countries to delay the second dose in order to provide the initial one to as many people as possible.
Arnon Afek, Sheba’s deputy director general, said the “research supports the British government’s decision to begin inoculating its citizens with a single dose of the vaccine.” The UK’s Joint Committee on Vaccination and Immunisation issued a recommendation in December that vaccinating more people with the first dose of BNT162b2, or AstraZeneca’s COVID-19 vaccine AZD1222, is now a priority above offering others their second dose. At the time, the committee said that as protection is obtained around two weeks after the first dose with both vaccines, the move “will provide the greatest public health benefits in the short term and save more lives.”