Oxford says COVID-19 vaccine 76% effective for 3 months after one shot

FILE PHOTO: A vial of the Oxford University/AstraZeneca COVID-19 vaccine is seen at the Lochee Health Centre in Dundee, Scotland, Britain January 4, 2021. Andy Buchanan/Pool via REUTERS

LONDON (Reuters) – The COVID-19 vaccine developed by Oxford University and AstraZeneca has 76% efficacy 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Oxford University said the findings of the pre-print paper, which had not been peer-reviewed, supported Britain’s decision to extend the interval between initial and booster doses of the shot to 12 weeks.

Britain has decided to give as many people as possible some protection by lengthening the amount of time between initial shots and booster shots of COVID-19 vaccines.

AstraZeneca has welcomed the move, saying flexibility to extend the time between doses is the best strategy for the shot.

The results, gathered from trials in Britain, Brazil and South Africa, indicated some protection was given after one shot and that immune responses were boosted with a longer interval to the second dose among participants aged 18 to 55 years.

“Vaccine efficacy after a single standard dose of vaccine from day 22 to day 90 post vaccination was 76%, and modelled 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.

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