AstraZeneca COVID Vaccine is 100% Effective at Preventing Severe Disease

Mar. 22, 2021

According to interim clinical trial results, the COVID vaccine developed by AstraZeneca and the University of Oxford is 100% effective at preventing severe COVID and 76% effective at preventing milder infections. The U.S. trial showed no safety concerns of any kind related to the vaccine – including risk of blood clotting. 

Final analysis from the U.S. phase 3 clinical trial is expected in the next few weeks at which point AstraZeneca is expected to apply for FDA approval. Vaccine could be available to Americans as early as April and will be the fourth effective COVID vaccine to gain approval. 

“It’s gratifying to see how well this vaccine was tolerated and how well it protected people from severe disease,” says Ann R. Falsey, M.D., co-lead principal investigator of the U.S. clinical trial and co-director of the URMC Vaccine and Treatment Evaluation Unit. “After working on the front lines last March, to see none of Astrazeneca vaccinated participants in this trial ending up in the hospital with COVID is a huge relief. It is amazing how well this vaccine works.” 

These results draw on data from 190 symptomatic COVID cases out of 32,449 volunteers at 88 sites across the U.S., including over 850 local volunteers who participated at the University of Rochester Medical Center (URMC) site. URMC joined the study on July 27, 2020, led by Falsey and Angela Branche, M.D., who co-directs the URMC Vaccine and Treatment Evaluation Unit alongside Falsey, as well as Michael Keefer, M.D., who leads the URMC HIV Vaccine Trials Unit. 

The phase 3 trial shows that the Oxford-AstraZeneca vaccine, known as AZD1222, is 100% effective at preventing hospitalizations and death, and 76% effective at preventing any COVID symptoms. While earlier European studies failed to produce sufficient data on volunteers over 65 due to low enrollment, the U.S. study enrolled approximately 6,000 volunteers in this age group and found that the vaccine protected this group just as well as others – with 85% efficacy. 

The U.S. independent data safety monitoring board also thoroughly investigated any enhanced risk of blood clotting in light of recent concerns raised in Europe. The board found no increased risk of clotting among the 21,583 participants who received at least one dose of the vaccine and no safety concerns related to the vaccine overall.

“As nations around the world struggle to vaccinate their populations, these results are great news,” says Branche. “More analysis and review is needed, but I am hopeful that this vaccine will soon be added to the existing arsenal of safe, approved COVID vaccines.” 

Once the FDA grants emergency use authorization, all trial volunteers – including those who participated locally – will be able to find out whether they received vaccine or placebo through the study. Anyone who received placebo will be offered the vaccine through the study.