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Amid supply snafu, new data show AstraZeneca’s COVID-19 shot is more effective with doses 12 weeks apart

February 2, 2021 Eric Sagonowsky


While supply constraints have hung over the rollout of the AstraZeneca COVID-19 vaccine in Europe, last week, CEO Pascal Soriot offered one way officials could make the most of available doses. And now AZ has more data to support the idea. 

Speaking with reporters after AstraZeneca’s COVID-19 vaccine scored a European authorization last week, Soriot pointed out that the label allows the second dose to be administered between 4 and 12 weeks after the first.

Officials could use all available doses to vaccinate as many people as possible now, he suggested, without reserving booster doses. Before 12 weeks passed, more supply would arrive to cover the boosters and start a new round of vaccinations.

In fact, waiting could be even better. New data show the vaccine was 54.9% effective in trial participants who received their second standard dose within 6 weeks of the first. For those who got a second standard dose 12 weeks or more after the first, efficacy was a much higher 82.4%.

Plus, waiting wouldn’t be a big risk. A standard dose of the vaccine is 76% effective between 22 days and 90 days after the first dose, which means people would be protected while waiting for their boosters. The analysis, which drew on data from an ongoing U.K. trial, was published in Preprints with The Lancet. 

Overall, the vaccine was 66.7% effective 14 days after trial participants received their second dose. 

RELATED: AstraZeneca’s COVID-19 shot scores European authorization as production holdups linger 

The team also ran weekly COVID-19 diagnostic tests on trial participants and found the first dose cut the number of positive tests by 67%. The data suggest the vaccine could have a “substantial impact on transmission by reducing the number of infected individuals in the population,” the researchers wrote. 

In earlier phase 3 results unveiled in November, AstraZeneca’s vaccine was 70% effective overall. A dosing error yielded a higher result in a subset of participants, though: For people who received a half dose followed by a full dose, vaccine efficacy was 90%.   

The trial results prompted AZ to run another study for a potential emergency use authorization in the U.S. That study is set to read out this month. 

RELATED: AstraZeneca’s COVID-19 vaccine 70% effective, shares fall 

The analysis comes as European officials work through the rollout of the vaccine amid supply shortfalls. After the recommendation, Soriot said the shot’s flexible dosing regimen allows officials to vaccinate one person with each dose AZ delivers. Then, people could get their second shot from a separate shipment up to three months later, he said. 

AstraZeneca is set to deliver 40 million doses of the vaccine in the first quarter, European officials said Sunday. That was an increase from a prior, large reduction, but only half of AZ’s original target. 



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