In one study, published on a preprint server in February, scientists reviewed the health records of about 1.1 million people over 60 who had received a fourth dose and compared them with those who had received just three doses. They found that the rate of confirmed infections, as well as that of severe illness, was lower in people who had gotten their fourth shot.
The second study, published Wednesday in The New England Journal of Medicinelooked at Israeli health care workers of all ages and found that both Pfizer’s and Moderna’s fourth shots bolstered antibody levels, though they were not very good at preventing infection.
Experts, however, cautioned that the available data is still preliminary and has not yet shown how long the benefits of a fourth dose will last.
If the shots are authorized for seniors, how should they think about timing them?
Experts tracking Covid-19 are careful not to give specific advice on when to get a fourth dose when the safety and efficacy data are still limited.
If another surge is just around the corner, for instance, seniors may benefit from getting an extra shot as soon as it’s authorized. But if the next wave does not occur until the summer or even the fall, getting a booster now could backfire because the recipients’ immunity might start to wane by the time they need protection the most. Current vaccines are based on the original strain of the coronavirus, so getting a booster now may also do little to protect against future variants.
“It would be great if we knew exactly when the next wave was going to be so we could vaccinate people beforehand,” said Dr. Amy Sherman, an infectious disease physician at Brigham and Women’s Hospital in Boston. “But I think we’re not quite at the point where we know a clear seasonality, and we know the exact tempo and dynamics of Covid and newer variants.”
That being said, if a fourth shot is authorized for adults over 65, and it has already been several months since they got their first booster, “I would start thinking about whether I need a booster now,” Dr. del Rio said.