The University of Oxford's coronavirus vaccine offers protection of 76% up to 12 weeks after a single dose and may reduce transmission by 67%, according to a new study.
After the second dose, vaccine efficacy from two standard doses is 82.4% with the three-month interval being used in the UK, researchers from the University of Oxford say.
The data from the study, which has not yet been peer reviewed, supports the four to 12-week prime-boost dosing interval that many global regulators have recommended.
Analyses of positive coronavirus swabs in the UK population suggest the vaccine may have a substantial effect on transmission of the virus, with a 67% reduction in positive swabs among those vaccinated with the Oxford/AstraZeneca jab.
Before these results, little was known about how effective the Covid-19 vaccines were at preventing transmission of the disease.
Researchers at the University of Oxford have published the preprints, which reveal that the vaccine efficacy is higher with longer intervals between doses, and that a single dose of the vaccine is 76% effective from 22 to up to 90 days post-vaccination.
Professor Andrew Pollard, chief investigator of the Oxford Vaccine Trial, and study co-author, said: "These new data provide an important verification of the interim data that was used by more than 25 regulators including the MHRA (Medicines and Healthcare products Regulatory Agency) and EMA (European Medicines Agency) to grant the vaccine emergency use authorisation.
"It also supports the policy recommendation made by the Joint Committee on Vaccination and Immunisation (JCVI) for a 12-week prime-boost interval, as they look for the optimal approach to roll out, and reassures us that people are protected from 22 days after a single dose of the vaccine."