New research has shown that the Pfizer vaccine generates a robust immune response after one dose, opening up the possibility that the second dose of the vaccine can be delayed for longer than first thought, according to The Wall Street Journal.
The discovery could influence decisions being considered by some governments to give more people their first dose, instead of holding back the vaccine to give people who have had their first shot the second shot in the series.
The peer-reviewed study conducted by the Sheba Medical Center in Ramat Gan, Israel, showed the first dose of Pfizer’s vaccine was 85% effective in preventing symptomatic disease by 15 to 28 days after it was administered.
That level of protection, researchers suggest, would be a valid reason to delay administering a second dose of the vaccine in favor of vaccinating more people with a first dose.
According to the Lancet, where the research was published, the study followed about 9,000 people and found a 75% reduction in both symptomatic infections and those without symptoms, after participants were given the first shot.
In addition to the possibility of delaying second doses for longer, researchers at Sheba Medical Center in Ramat Gan, Israel, found that the Pfizer vaccine did not need the ultracold storage temperatures that the company first said were required.
When seeking permission for an emergency use authorization, Pfizer told the U.S. Food and Drug Administration that the vaccine must be stored at temperatures ranging between minus 112 and minus 76 degrees Fahrenheit.
On Friday, Pfizer said it will be asking the FDA to approve an amended plan to store the vaccine at temperatures commonly found in pharmaceutical freezers and refrigerators. Pfizer said it submitted new data that shows the vaccine is stable for two weeks in a refrigerator set between minus 13 and 5 degrees Fahrenheit.
Health officials in the United Kingdom recently approved delaying the time between the first and second shots of the Pfizer vaccine from three weeks to 12 weeks, saying research suggested that extending the time between shots did not diminish the vaccine’s effectiveness.
The Centers for Disease Control and Prevention likewise has issued guidance saying that a delay in getting the second dose of either the Pfizer or Moderna vaccines would not have an impact on the vaccines’ effectiveness.
According to clinical trial results Pfizer provided to the FDA, its vaccine showed 52.4% effectiveness after one shot. However, that research did not show the effectiveness of the vaccine two weeks after the shot was given. The effectiveness jumped to 94% more than two weeks out from the first shot and 95% efficacy a week after the second shot.
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