WASHINGTON — Pfizer's COVID-19 vaccine is 85% effective just 15-28 days after the first dose, according to a new study out of Israel, adding further debate over whether second doses should be delayed to vaccinate more people.
The study involved health care workers at Sheba Medical Center in Israel and was published in The Lancet journal.
It found Pfizer's vaccine was 85% effective in preventing symptomatic COVID-19 cases and 75% effective when asymptomatic cases were included too.
One thing the study didn't look at was how long a single dose can provide protection against the coronavirus. The researchers stress more data is needed on the long-term effectiveness of single doses to determine whether second doses should be delayed.
Both the Pfizer and Moderna vaccines were tested on a two-dose regimen, with the first and second doses 21 days apart for Pfizer and 28 days apart for Moderna.
With COVID-19 vaccine supplies limited, Britain has moved to a contentious 12-week dosing schedule for Pfizer's vaccine, despite concerns from other European countries.
Last month, the Food and Drug Administration said suggesting any changes to the FDA-authorized dosing plan would be premature and warned that 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."
Meanwhile, Pfizer announced Friday that it had submitted new data showing that its vaccine could be stored at regular freezer temperature for two weeks, instead of having to keep it constantly at ultra-cold temperatures. Pfizer said it submitted the data to the FDA to support a proposed update to the U.S. Emergency Use Authorization.