Pfizer COVID-19 vaccine 85% effective after single dose, Israeli researchers find

A vaccine developed by Pfizer-BioNTech cut symptomatic COVID-19 disease by 85% after the first dose, according to Israeli researchers.

Findings were outlined in correspondence published in The Lancet on Friday, drawing on results from 7,214 health care workers at the Sheba Medical Center. Researchers found the 85% reduction in disease 15 to 28 days after the first dose, and reported a 75% drop in infections within the same time period.

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"Our data show substantial early reductions in SARS-CoV-2 infection and symptomatic COVID-19 rates following first vaccine dose administration," study authors wrote.

The drop in disease after a single dose could bolster an approach to space out the dosing regimen amid vaccine supply issues, the team noted. However, most of the vaccinated cohort was "young and healthy," warned Sheba epidemiologist Gili Regev-Yocha, per Reuters.

The findings stack up against an overall 95% vaccine efficacy for a two-dose regimen administered 21 days apart, as previously reported by Pfizer-BioNTech. In a statement sent to Fox News on Friday, Pfizer said it is leading an "analysis of the vaccine’s real-world effectiveness at several locations worldwide, including Israel."

 "We are particularly looking at real world data from Israel to understand any potential impact of the vaccine to protect against COVID-19 arising from emerging variants," the statement reads.

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Results from the Israeli researchers come after two Canadian researchers penned a letter in the New England Journal of Medicine Thursday, after they analyzed Pfizer's vaccine data submitted to the U.S. Food and Drug Administration. While Pfizer reported 52.4% efficacy between the first and second dose, the Canadian researchers argued the immune system was still ramping up its response. The Canadian researchers, Drs. Danuta Skowronski and Gaston De Serres, instead found a 92.6% efficacy two weeks after the first dose, before the second dose.

"With such a highly protective first dose, the benefits derived from a scarce supply of vaccine could be maximized by deferring second doses until all priority group members are offered at least one dose," Skowronski and De Serres wrote. They said that while the degree of protection offered after a single dose is unclear, the benefits of a first dose spread further across populations of at-risk individuals far outweigh the "little added benefit" from second doses administered within a month.

They called postponing of a second dose amid supply shortages a "matter of national security," potentially contributing to thousands of virus-related hospitalizations and deaths in the coming months.

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In a separate joint statement issued last month, FDA Commissioner Dr. Stephen Hahn and Dr. Peter Marks, head of the FDA's Center for Biologics Evaluation and Research, advised the public to adhere to the authorized dosing and vaccination schedules: two-doses 21 days apart for Pfizer/BioNTech COVID-19 vaccine and two-doses 28 days apart for the Moderna COVID-19 vaccine.

"At this time, suggesting changes to the FDA-authorized dosing or schedules of these vaccines is premature and not rooted solidly in the available evidence," reads the statement. "Without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19."