Newly released data confirmed on Tuesday that Moderna's coronavirus vaccine is highly protective, setting the stage for its emergency authorization this week by federal regulators and the start of its distribution across the country.
The Food and Drug Administration intends to authorize use of the vaccine on Friday, people familiar with the agency's plans said. The decision would give millions of Americans access to a second coronavirus vaccine beginning as early as Monday.
Moderna's vaccine worked equally well in white volunteers and in communities of color. There was also no significant difference between its protection for men and women, or between healthy volunteers and those at risk of severe Covid-19 who had conditions like obesity and diabetes. For people 65 and older, the trial provided an estimated efficacy of 86.4 percent, lower than the overall estimate of 94.1 percent. But the apparent difference was not statistically significant.
So far, two potential differences between the vaccines have emerged from the F.D.A.'s reviews, but the findings may reflect a shortage of data rather than genuine differences. The Pfizer-BioNTech trial showed that their vaccine started to protect against the coronavirus within about 10 days of the first dose. The trial of Moderna's vaccine, by contrast, did not reveal such a striking effect after the first dose.
But fewer cases of Covid-19 occurred among trial participants in the early days of the Moderna trial, making it harder to measure differences between the vaccinated group and the placebo group. In any case, health officials have said that for both vaccines, two doses are essential for full protection.
A second difference involves the ability to prevent severe disease. Moderna produced more evidence that its vaccine can do so, according to the review. In its trial, 30 volunteers developed severe cases of Covid. All of them were in the placebo group, with no cases among the people who were vaccinated.
In the Pfizer-BioNTech trial, the findings were less compelling. There were 10 severe cases in the placebo group and one in the vaccinated group. Those numbers are too small to gauge the vaccine's ability to prevent serious illness.
"The available data for these outcomes did not allow for firm conclusions," the F.D.A. said.
The documents published Tuesday made clear that side effects were particularly common after the second dose, but typically lasted only a day. Experts say people may need to take a day off work after getting the shot.
Moderna has requested authorization to vaccinate people 18 and older, like those in its study. The Pfizer-BioNTech vaccine was authorized for people as young as 16, because the trial had some younger volunteers. Both companies are running trials on children as young as 12 and have plans to start studying even younger children.
Distribution of about six million doses could then begin next week, significantly adding to the millions of doses already being shipped by Pfizer and BioNTech, the companies that developed the first coronavirus vaccine given emergency clearance just last Friday. Health care workers received the first shots on Monday of the Pfizer-BioNTech vaccine, which has an efficacy rate of 95 percent.
The federal government signed deals last summer with Moderna and Pfizer to deliver a total of 200 million doses in the first quarter of 2021. Because both vaccines require two doses, those contracts guaranteed enough doses for 100 million people.
Last week the government announced that it had purchased another 100 million doses from Moderna for the second quarter, increasing the number of Americans who can be vaccinated to 150 million. But that still leaves the question of how and when the roughly 180 million other Americans will be covered.
Moderna Vaccine Is Highly Protective and Prevents Severe Covid-19, Data Show
The positive review likely ensures that the F.D.A. will grant emergency authorization for a second coronavirus vaccine this week for millions of Americans.
