The COVID-19 vaccine produced by Oxford University and AstraZeneca have 76% efficiency against symptomatic infection for three months after a single dose, with greater effectiveness when a second is given later, a study showed on Tuesday. Oxford University said the conclusions of the pre-print paper, which had not been peer-reviewed, supported Britain’s decision to extend the interval between primary and booster doses of the shot to 12 weeks.
The results, collected from tests in Britain, Brazil, and South Africa, showed some protection was given after one shot and those immune responses were increased with a longer interval to the second dose among participants aged 18 to 55 years.
Britain has chosen to give as many people as possible some protection by extending the amount of time between initial shots and booster shots of COVID-19 vaccines. AstraZeneca has embraced the move, saying flexibility to extend the time between doses is the best plan for the shot.
“Vaccine efficacy after a single standard dose of vaccine from day 22 to day 90 post-vaccination was 76%, and modeled analysis indicated that protection did not wane during this initial 3 month period,” Oxford academics said.
The paper said that vaccine efficacy was 82.4% with 12 or more weeks to the second dose, compared to 54.9% for those where the booster was given under 6 weeks after the first dose.