The recently released documents, which include the FDA’s first technical analysis of the company’s 45,000-person clinical trial, provided evidence that the vaccine was safe, with side effects noticeably milder than the Pfizer and Moderna vaccines and with no reports of reactions severe allergies such as anaphylaxis.
Vaccine protection was consistent among black, Hispanic and white volunteers, and also at different ages. The study estimated a lower effectiveness, 42.3 percent, for people over 60 who had risk factors like heart disease or diabetes, a number that came with a great deal of statistical uncertainty, the FDA noted.
Dr. James Burke, a study design specialist at the University of Michigan School of Medicine, warned that the results found in small subgroups may be due to chance. “We are more wrong than right,” he said. “Therefore, we must always act with great care.”
He noted that the trial recorded only 41 cases of Covid-19 in 6,667 people over 60 with comorbidities. “Common sense makes it very clear that we cannot make very robust estimates with such a small number of results,” said Burke.
Preliminary data suggest that the protective effects of the vaccine increase in the weeks after vaccination. After 42 days, for example, only one person vaccinated received Covid-19, while 13 people in the placebo group did, which translates into an 92.4% effectiveness rate. It is unclear how long the vaccine protection will last before it decreases, an uncertainty that hangs over all vaccines against coronavirus, as they have started to be tested in recent months.
Although several vaccines can protect people from becoming sick with Covid-19, it is not clear whether vaccines can also prevent people from becoming infected and spread the virus to others, leading to a debate about how quickly society can return to normal after the start of inoculations.
The Moderna trial found some evidence that vaccinated people were less likely to develop an infection without symptoms. And AstraZeneca found that its vaccine cut asymptomatic infections in half.