The drugmaker Pfizer announced on Monday that early analysis of its coronavirus vaccine trial suggested the vaccine was robustly effective in preventing Covid-19, a promising development as the world has waited anxiously for any positive news about a pandemic that has killed more than 1.2 million people.

Pfizer, which developed the vaccine with the German drugmaker BioNTech, released only sparse details from its clinical trial, based on the first formal review of the data by an outside panel of experts.

The company said that the analysis found that the vaccine was more than 90 per cent effective in preventing the disease among trial volunteers who had no evidence of prior coronavirus infection. If the results hold up, that level of protection would put it on par with highly effective childhood vaccines for diseases such as measles. No serious safety concerns have been observed, the company said.

Pfizer plans to ask the Food and Drug Administration for emergency authorization of the two-dose vaccine later this month after it has collected the recommended two months of safety data. By the end of the year it will have manufactured enough doses to immunize 15 to 20 million people, company executives have said.