New Pfizer Results: Coronavirus Vaccine Is Safe and 95% Effective

The companies said that out of 170 cases of Covid-19, 162 were in the placebo group, and eight were in the vaccine group. Out of 10 cases of severe Covid-19, nine had received a placebo.

Pfizer and BioNTech said that the vaccine’s efficacy was consistent across age, race and ethnicity. The most common serious adverse event was fatigue, with 3.7 percent of volunteers reporting tiredness after they took the second dose. Two percent of volunteers reported a headache after the second dose. Older adults reported fewer and milder side effects, the companies said.

“It’s pretty amazing,” said Akiko Iwasaki, an immunologist at Yale University. She said the results in people over 65 were the most promising. “We know from the influenza vaccine that it’s very difficult to achieve protection in this age group with vaccines,” she said, so 94 percent efficacy in that group “is really remarkable.”

Federal health officials have said the first doses of the vaccines will most likely go to groups like health care workers who are at high risk for exposure, as well as to people who are most vulnerable to the disease, such as older people.

Dr. Saad B. Omer, the director of the Yale Institute for Global Health, said the results showing the vaccines protected people from severe disease was also good news, because with such limited availability initially, the first goal will be not to stop transmission of the disease, but to prevent people from becoming extremely ill. “So that is very reassuring,” he said.

He called on Pfizer to quickly release a more detailed analysis of the data — beyond the initial news release — so that scientists could more thoroughly evaluate the results. The companies have said they plan to submit the results for review in a scientific journal, a process that can take weeks or months. “These are not normal times, this is a pandemic, and major policy is being made,” Dr. Omer said. “It’s always better to make policy on scientific data, not a press release.”

In addition to the results of its clinical trial, Pfizer said it was ready to submit to the F.D.A. two months of safety data that the agency had recommended, as well as detailed manufacturing records showing the company can consistently produce high-quality batches of its product. The F.D.A. will review the data and ask an outside panel of vaccine experts to weigh in on the application, a process that could take weeks.