By Jenny Strasburg

LONDON -- The Covid-19 vaccine being developed by the University of Oxford and AstraZeneca PLC was found to be as much as 90% effective in preventing infections without serious side effects in a large clinical trial, the partners said Monday.

AstraZeneca said there were no serious safety events related to the vaccine and it was well tolerated across different dosing regimens. Efficacy ranged from 62% to 90% depending on the dosage given, the partners said. AstraZeneca and Oxford said the average efficacy in the analysis was 70%.

The trials were held in the U.K. and Brazil. Late-stage clinical trials of the vaccine are continuing in the U.S. following a trial pause there that spanned most of September and October.

The results bode well for the eventual availability of a third Western-developed vaccine to battle Covid-19, after shots developed by Moderna Inc. and jointly by Pfizer Inc. and Germany's BioNTech SE were found to be more than 90% effective in late-stage trials.

Pfizer and BioNTech late last week said they asked for approval from the U.S. Food and Drug Administration to permit use of their vaccine.

AstraZeneca and Oxford's vaccine stands out among the leading Western candidates. The partners committed to selling it without profit during the pandemic and promised to distribute it across a much wider geographic footprint, including in large parts of the developing world.

The European Medicines Agency, which authorizes new medicines for sale in the European Union, said in early October that it had begun a rolling review of the Oxford vaccine in order to speed up a potential approval. A rolling review allows regulators to evaluate preliminary data such as those from lab experiments before final-stage clinical trials are completed.

Canada has also begun a rolling review of the vaccine, according to a statement in early October by the country's health agency.

Officials in the U.K., which is transitioning out of the EU, say they have the power to authorize use of a Covid-19 vaccine in the U.K. before year-end, if they choose. The U.K. also has been reviewing Oxford and AstraZeneca's vaccine data, on a rolling basis, since early November.

The Oxford-AstraZeneca vaccine trials ultimately will enroll as many as 60,000 participants globally.

Write to Jenny Strasburg at jenny.strasburg@wsj.com

(END) Dow Jones Newswires

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