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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.

Go deeper

Jan 29, 2021 - World

EU grants conditional approval of AstraZeneca vaccine

Photo: Sunil Ghosh/Hindustan Times via Getty Images

The European Commission on Friday granted conditional approval of the Oxford-AstraZeneca coronavirus vaccine for people 18 years and older.

Why it matters: This is the third vaccine to receive approval from the commission, coming hours after the Emergency Medicines Agency recommended its authorization.

Jan 29, 2021 - Health

Ex-CDC director Tom Frieden on the next COVID-19 vaccines

Americans fortunate enough to receive COVID vaccines now, outside of clinical trials, are getting shots made by either Pfizer or Moderna. But newly released data from Novavax and Johnson & Johnson suggests that more vaccines could be on the way, with J&J's requiring a single dose.

Axios Re:Cap digs into the news and why it matters with Tom Frieden, former head of the CDC, as COVID-19 variants spread globally.

Updated Oct 21, 2021 - Politics & Policy

Coronavirus dashboard

Illustration: Aïda Amer/Axios

  1. Vaccines: Pfizer booster has 95.6% efficacy, large study shows — FDA authorizes mix-and-match for booster shots — J&J expects $2.5 billion of vaccine sales this year.
  2. Health: Cases and deaths keep falling — White House unveils plan to "quickly" vaccinate kids ages 5-11 — The global coronavirus vaccine gap — Gates Foundation to send $120 million of antiviral pills to lower-income countries.
  3. Politics: Reports: Brazil leader to be accused of crimes against humanity over COVID — Puerto Rico leads U.S. vaccination rates — Hawaii invites fully vaccinated travelers to return from Nov. 1.
  4. Education: Education secretary reveals limits to Biden’s mask push on states — LA extends deadline for school employee vaccinations — Parent sues Wisconsin school district after child tests positive.
  5. Variant tracker: Where different strains are spreading.