Analysis of data from a phase 3 trial of the vaccine developed by Oxford University showed that it was 90 percent effective when half a dose was administered followed by a full dose. In another dosing regimen, when two full doses were administered, the vaccine was 62 percent effective, researchers said, resulting in combined average efficacy of 70 percent.

There were no hospitalized or severe cases in anyone who received the vaccine, researchers said. More analysis is needed to determine how long the protection rendered by the vaccine could last.

The creators of the AstraZeneca vaccine, which uses a weakened version of a common cold virus, said it could be administered in existing healthcare settings, like medical clinics and local pharmacies, and stored at refrigerator temperature of 2 to 8 degrees Celsius (36 to 46 degrees Fahrenheit) for at least six months, making its distribution easier.