AstraZeneca and Oxford University’s COVID-19 vaccine was 79% effective in a large US trial at preventing symptomatic illness, and was 100% effective against severe or critical disease and hospitalisation, the drug maker said.

The fresh data comes after many countries resuming use of the vaccine after the European Medicines Agency (EMA) and the World Health Organization (WHO) said the benefits outweighed the risks following investigations into reports of blood clots.

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AstraZeneca said an independent safety committee conducted a specific review of the blood clots in the US trial, as well as cerebral venous sinus thrombosis (CVST), which is an extremely rare blood clot in the brain, with the help of an independent neurologist.

The London-listed firm said the panel found “no increased risk of thrombosis or events characterised by thrombosis among the 21,583 participants receiving at least one dose of the vaccine. The specific search for CVST found no events in this trial.”