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By Julie Steenhuysen

CHICAGO (Reuters) -AstraZeneca Plc’s COVID-19 vaccine demonstrated 74% efficacy at preventing symptomatic disease, a figure that increased to 83.5% in people aged 65 and older, according to long-awaited results of the company’s U.S. clinical trial published on Wednesday.

A total efficacy score of 74% was less than the March interim 79% reported by British drugmaker AstraZeneca. AstraZeneca’s U.S. clinical trial results were published on Wednesday. AstraZeneca (NASDAQ): revised the result to 76% days later after an unusual public response from health officials claiming that the number was not based upon “outdated information”.

More than 26,000 people in America, Chile, and Peru were included in this study. They received the two doses approximately one month apart. These results were published by the New England Journal of Medicine.

More than 17.600 of the participants received the vaccine. This compares to the 8 cases in which there were severe cases or serious symptoms. Two deaths occurred in the placebo-treated group, but no one was reported among the recipients of the vaccine.

Anna Durbin (Johns Hopkins University vaccine researcher and one of its investigators) said that the final result was “pleasantly surprising”. It was extremely protective against serious disease and hospitalization,” Durbin said.

AstraZeneca’s vaccine was created with Oxford University scientists. There have been no reports of severe, but still rare, blood clotting side effects such as thrombosis and thrombocytopenia.

AstraZeneca stated in July that it would file for approval from the U.S. Food and Drug Administration rather than seeking emergency authorization. Pascal Soriot, chief executive of AstraZeneca, stated that he hopes the vaccine can still be used in the United States. However the wait was longer than anticipated.

The company is exploring booster doses for people whohave already been vaccinated with two doses of either its ownshot or mRNA-based vaccines from Pfizer/BioNTech or Moderna (NASDAQ:).

Vaxzevria is a vaccine that can be used in over 170 countries. The spokesperson for the company stated that they expect to apply for U.S. authorization later in this year.

Durbin stated that she doesn’t expect Vaxzevria will be used in America much, but FDA approval does give the company “gravity.”