The advisory committee is also likely to consider whether Moderna's protection from serious illness and hospitalization may wane. Booster proponents argue that the potency of Moderna decreases similar to that of Pfizer, which is based on the same technology, only more slowly because the starting dose is significantly stronger than Pfizer's and the interval between the first two shots is a week longer .
"The basic question is what do we want to do?" said Dr. El Sahly. “Both Moderna and Pfizer seem to have subsided in mild to moderate illnesses, especially the Delta variant. So if that is the goal, a booster is needed. "
"If we just want to prevent a serious illness that brings people to the hospital," she said, "that's another math."
The F.D.A. has not yet published its review of Johnson & Johnson booster data. In its application for booster approval, however, the company provided information from two studies.
In a study announced in August, the company gave 17 volunteers a second vaccination six months after the first. In these subjects, Johnson & Johnson reported, the antibody levels against the coronavirus rose twelve times higher than after the initial dose. Researchers haven't determined exactly how much protection this flare will offer against Covid-19.
The second study, which Johnson & Johnson reported last month, showed that a booster can actually improve protection. In November 2020, the company started a clinical trial with 32,000 volunteers, this time with a second dose of the vaccine two months after the first.
The company announced that in the portion of the study that took place in the United States, its effectiveness increased to 94 percent. Globally, the increase was more modest at 75 percent – roughly the same effectiveness reported for a single dose in the US over the winter. Against severe to critical Covid-19, two shots had an effectiveness of 100 percent.
Noah Weiland contributed coverage from Washington, D.C.; Amy Schoenfeld Walker of Trumbull, Connecticut; and Carl Zimmer of Guilford, Conn.