Nov 25, 2020 - Health

Confusion remains over AstraZeneca vaccine

Medical syringes are seen with AstraZeneca and University of Oxford logos displayed on a screen in the background in this illustration photo taken in Poland
Medical syringes are seen with AstraZeneca and University of Oxford logos displayed on a screen in the background in this illustration photo taken in Poland. Photo: Jakub Porzycki/NurPhoto via Getty Images

Experts are still trying to make sense of AstraZeneca and Oxford University’s coronavirus vaccine.

The big question: Oxford and AstraZeneca said their vaccine was 90% effective in people who got a half dose followed by a full dose, and 62% effective in people who got two full doses. Why would a lower dose be more effective?

The intrigue: The 90% figure has gotten a lot more attention because it’s a lot more impressive, but it may be a somewhat distorted picture.

  • In clinical trials for the vaccine, the half-dose version — the one with 90% efficacy — was tested on a group that didn’t include anyone older than 55, Bloomberg reports from a briefing by Operation Warp Speed officials.
  • The half-dose version was a mistake, owing to some under-filled vials.

The other side: Some researchers believe the difference is real, and not a data issue.

  • Smaller doses may be more effective in stimulating certain parts of the body’s immune response, or that a larger dose may blunt the body’s response to some parts of the virus, according to an article in Nature.

Our thought bubble: All we’ve seen so far, for all three vaccines, are press releases. Experts still need to see scientific, peer-reviewed findings.

  • “I'm glad this is not the first vaccine to read out, because it is awfully confusing for experts and non-experts alike,” University of Florida professor Natalie Dean, an expert on vaccine clinical trial design, said in a Twitter thread.
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