Feb 19, 2021 - Health

Data finds Pfizer vaccine highly effective after first dose, can be stored in normal freezers

Pfizer vaccine

Photo: Robert Michael/picture alliance via Getty Images

Pfizer's coronavirus vaccine may be more effective after just one shot than researchers had previously realized, and can be stored for two weeks at standard temperatures typically found in pharmaceutical freezers and refrigerators, according to new data.

Why it matters: The findings about first-dose efficacy, which appear in a new analysis published in The Lancet, appear to support a strategy of delaying second shots in order to make the most of limited supplies. That's what the U.K. has done, and some experts have called for a similar approach in the U.S.

Separately, Pfizer and BioNtech's announcement that vaccine vials can be stored and transported at -25°C to-15°C (-13°F to 5°F) could allow the vaccine to be handled by ordinary pharmacies that aren't equipped with ultra-low freezers, which have been an impediment in the vaccine rollout.

  • The companies said that they had submitted a proposed update to the FDA's emergency use authorization to allow the vaccine to be stored at these temperatures "as an alternative or complement to storage in an ultra-low temperature freezer."

Details: Pfizer's clinical trials initially showed that its vaccine prevented roughly 52% of infections after one dose, rising to 95% after two doses.

  • The new research published in The Lancet, however, found that the first shot of Pfizer's vaccine actually prevented about 75% of infections, and 85% of symptomatic infections, up to 28 days after it was administered.
  • The findings were based on an evaluation of about 9,000 people in Israel, which has vaccinated over two-thirds of its adult population, The Wall Street Journal reports.

Yes, but: There are some limitations to this study and its implications for delaying second doses.

  • Although the first dose appeared to be more powerful than originally anticipated, researchers still don't know how long its effects will last.
  • Pfizer recommends getting the second dose 21 days after the first one. The Israeli study measured the efficacy of the first shot within 15 to 28 days of its administration — not a significant delay. And most participants in the trial did receive their second shots, the authors told the WSJ.

The big picture: Most of the people in this study got their second doses, and got those doses on time. Second doses were not delayed in this case, and so this study does not directly answer the question of what happens when you delay second doses.

  • The findings will bolster calls to delay second doses because they indicate that first doses are more effective than we realized — making a compelling case to get that level of protection to as many people as possible as quickly as possible, to save lives and bring the pandemic under control.
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