AstraZeneca, Oxford Covid-19 Vaccine Up to 90% Effective in Late-Stage Trials

LONDON—AstraZeneca PLC and the University of Oxford said their Covid-19 vaccine was as much as 90% effective in preventing infections without serious side effects in large clinical trials, boosting hopes that a third Western-developed shot could be authorized for use before the end of the year.

The partners said Monday that there were no confirmed serious safety events related to the vaccine and that it was well tolerated across different dosing regimens. Its efficacy ranged from 62% to 90% depending on the dosage given,…