AstraZeneca's COVID-19 vaccine was 70 percent effective at preventing infection from the virus in more than 11,000 participants in late-stage international trials, according to results published Dec. 8 in The Lancet.
The vaccine was only about 60 percent effective among people who received the standard two-dose regimen, but was 90 percent effective in those who received a half-dose the first round and a full dose the second round. About 2,700 volunteers were accidentally given a half-dose for their first shot and a full dose the second time. It's unclear if their better efficacy rate was a statistical fluke or if the lower dose prepped the immune system to be better protected, USA Today reported.
AstraZeneca and its partner Oxford University said they need more data from the trials to figure out if the half-dose, full-dose regimen is actually more effective.
AstraZeneca said the trial results were strong enough to apply for authorization from the U.K., European Union and elsewhere, but the U.S. will likely wait for results of a larger, 30,000 person trial being conducted in the U.S. to make a regulatory decision. Those results will likely come early next year, USA Today reported.
The Astraeneca trial also looked at whether the vaccine could prevent asymptomatic cases of COVID-19, and the results suggest it might, but weren't conclusive.
Three people in the British and Brazillian trials of AstraZeneca's COVID-19 vaccine candidate appeared to have a serious reaction to it, though the vaccine was ruled out as a cause by one person because the participant was in a placebo group, USA Today reported.
A second person had a fever of 104 after the first dose, but it only lasted for a day, and there was no reaction to the second dose. The third person developed transverse myelitis, a rare neurological disease, but it's unclear if the vaccine was the cause.