AstraZeneca's initial analysis of phase III data found that in individuals over 65 years of age, the vaccine's efficacy was 76%. In the trial's secondary endpoint -- prevention of severe or critical disease and hospitalization -- the efficacy rate was 100%. The vaccine was well tolerated, and no safety concerns related to the vaccine were identified.

Despite the positive initial analysis, controversy erupted on March 22 when the trial's independent data safety monitoring board notified federal authorities that it was concerned about the data collected in the trial, which it felt may have included outdated information that may have an effect on the reported efficacy.

AstraZeneca's new analysis appears to refute those concerns. The company's primary efficacy analysis from the phase III clinical study included the accrual of 190 symptomatic cases of COVID-19 from the 32,449 trial participants, an additional 49 cases to the previously announced interim analysis. Participants were randomized on a 2:1 ratio between the vaccine and placebo group.

"The primary analysis is consistent with our previously released interim analysis, and confirms that our COVID-19 vaccine is highly effective in adults, including those aged 65 years and over," said Mene Pangalos, executive vice president, BioPharmaceuticals R&D, a part of AstraZeneca. "We look forward to filing our regulatory submission for emergency use authorization in the U.S. and preparing for the rollout of millions of doses across America."

The company has presented the results to the data safety monitoring board and has reaffirmed that its primary analysis will be the basis for regulatory submission for emergency use authorization (EUA) of the vaccine candidate to the U.S. Food and Drug Administration (FDA) in the coming weeks.