The front-runners in the vaccine race seem to be working far better than anyone expected: Pfizer and BioNTech announced this week that their vaccine had an efficacy rate of 95 percent. Moderna put the figure for its vaccine at 94.5 percent. In Russia, the makers of the Sputnik vaccine claimed their efficacy rate was over 90 percent.

“These are game changers,” said Dr. Gregory Poland, a vaccine researcher at the Mayo Clinic. “We were all expecting 50 to 70 percent.” Indeed, the Food and Drug Administration had said it would consider granting emergency approval for vaccines that showed just 50 percent efficacy.

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The drug maker Pfizer announced on Monday that an 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.

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Late-stage coronavirus vaccine trials run by AstraZeneca and Johnson & Johnson have resumed in the United States after the companies said on Friday that serious illnesses in a few volunteers appeared not to be related to the vaccines.

Federal health regulators gave AstraZeneca the green light after a six-week pause, concluding there was no evidence that the experimental vaccine had directly caused the neurological side effects reported in two participants. The AstraZeneca news was first reported by The Wall Street Journal.

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