Another Vaccine Reaches 90% Efficacy

A volunteer participates in Oxford University's COVID-19 vaccine trial. Soweto, South Africa, June 28, 2020. Image: Felix Dlangamandla/Beeld/Gallo Images via Getty Images
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A volunteer participates in Oxford University's COVID-19 vaccine trial. Soweto, South Africa, June 28, 2020. Image: Felix Dlangamandla/Beeld/Gallo Images via Getty Images

The AstraZeneca/Oxford University COVID-19 vaccine has up to 90% efficacy against SARS-CoV-2—and would be easier to distribute than other promising candidates, according to interim results from a Phase 3 vaccine trial.
 
The trial looked into 2 dosing regimens, AP reports

  • A half dose followed by a full dose 1+ months later showed ~90% efficacy.
  • 2 full doses a month apart had 62% efficacy. 


Crucially: “The Oxford vaccine can be stored in the fridge, as opposed to the freezer…” says Oxford’s Peter Horby—a major advantage for global distribution.
 
But equitable distribution concerns go beyond cold storage. Rich countries have already bought up billions of future doses, while it could be years before poor countries get theirs.
 
Speaking yesterday at the G20 summit, Angela Merkel vowed to take up that issue with Gavi, the Vaccine Alliance, NPR reports. G20 leaders signed a communique pledging to help the poorest countries obtain vaccines and treatments, Politico reports.

  

Why does a lower first dose work better?

 
That may seem counterintuitive.
 
“With drugs, we expect that higher doses have bigger effects, and more side-effects,” said Peter Openshaw, professor of experimental medicine at Imperial College London. “But the immune system does not work like that.”
 
The BBC offered up a couple possibilities: The immune system may reject a bigger initial dose of the vaccine, which is built around the common cold virus. Also, a lower dose followed up with a higher dose may better mimic a real infection and trigger a more effective immune response.

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