The newly released documents, which included the FDA’s first technical analysis for the company’s 45,000-person study, showed the vaccine was safe, with significantly milder side effects than Pfizer and Moderna vaccines, and with no reports of severe allergic reactions such as Anaphylaxis.

The protection of the vaccine was the same among black, Hispanic, and white volunteers, and among different age groups. The study estimated a 42.3 percent lower effectiveness for people over 60 who had risk factors such as heart disease or diabetes. According to the FDA, this number was associated with a large statistical uncertainty.

Dr. James Burke, a study design expert at the University of Michigan’s School of Medicine, cautioned that the results found in small subgroups could turn out to be a random result. “We’re more wrong than right,” he said. “So we should always be very careful.”

He found that the study recorded only 41 cases of Covid-19 in 6,667 people over 60 with comorbidities. “Common sense makes it pretty clear that we cannot make very solid estimates with such a small number of results,” said Dr. Burke.

Preliminary data suggest that the vaccine’s protective effect increases in the weeks following vaccination. For example, after 42 days, only one vaccinated person received Covid-19, while 13 people in the placebo group did, giving an effectiveness rate of 92.4 percent. It’s not clear how long the vaccine’s protection will last before it wears off. This uncertainty hangs over all coronavirus vaccines as they have only been tested in the past few months.

Although multiple vaccines can protect people from contracting Covid-19, it’s unclear whether the gunshots can also prevent people from becoming infected and passing the virus on to others, leading to a debate about how quickly society will change after the start Vaccinations can return to normal.

Moderna’s study found some evidence that vaccinated people were less likely to develop an infection without symptoms. And AstraZeneca found that its vaccine reduced asymptomatic infections by about half.