Oxford finds AstraZeneca COVID-19 shot 76% effective in second, third month after single dose

In a pre-print paper yet to be peer-reviewed by members of the research community, Oxford Institute researchers supported the decision of the UK in increasing the interval between the first and booster doses of the Oxford-AstraZeneca COVID-19 vaccine, to 12 weeks. The study hasn't addressed concerns about a lack of efficacy data for the vaccine in the elderly, which are among the priority groups to be vaccinated in most countries, Britain included. The 12-week interval between doses was 'the optimal approach to roll out', according to the study.

The study claims that none of the 12,408 people vaccinated with a single dose of the vaccine was hospitalised with Covid-19 from 22 days after immunisation. The researchers reassured recipients of the vaccine that the protection from it begins 22 days after a single dose. From 22 days to 90 days after vaccination, a single dose of the vaccine was found 76 percent effective in preventing COVID-19 disease.

"Vaccine efficacy after a single standard dose of vaccine from day 22 to day 90 post-vaccination was 76 percent, and modelled analysis indicated that protection did not wane during this initial 3-month period," Oxford academics said in the preprint. The efficacy was 82.4 percent when the first and booster doses were 12 or more weeks apart, compared to 54.9 percent when the booster was given within six weeks of the first dose, the study said.

While Europe's medicine regulator has flagged that there isn't enough data to determine how well the vaccine will work in people aged over 55, but Britain has expressed confidence the vaccine works in all age groups. Of the countries vaccinating its population with the AstraZeneca vaccine, the UK has decided to vaccinate as many people as possible, as quickly as possible, by extending the amount of time between initial shots and booster shots. The main agenda behind this move was  to minimise the damage from multiple COVID-19 strains that are currently affecting Britain's population.

Oxford claims the vaccine also reduced transmission of SARS-CoV-2, with data suggesting as much as 67 percent reduction in the risk of a positive COVID-19 swab test among the participants in the British arm of the trial.