The advisory committee is also likely to consider whether Moderna’s protection against serious illness and hospitalization could weaken over time. Booster proponents claim that Moderna’s potency decreases just as much as Pfizer’s, which is based on the same technology, only slower because the initial dosage is significantly stronger than Pfizer’s and the interval between the first two shots is a week longer.
“The fundamental problem is, what are we trying to do?” said Dr El Sahly. “Both Moderna and Pfizer seem to have declined in mild to moderate disease, especially with the Delta variant. So if that’s the goal, then a booster is needed.”
“If we just want to prevent a serious illness that puts people in the hospital,” she said, “that’s another math.”
The FDA has not yet released its review of Johnson & Johnson’s booster data. But in its application for a booster authorization, the company provided data from two studies.
In a study announced in August, the company gave a second injection of the vaccine to 17 volunteers six months after the first. In these subjects, Johnson & Johnson reported, levels of antibodies to the coronavirus rose 12 times higher than after the starting dose. Researchers haven’t determined exactly how much protection that boost provided against Covid-19.
The second study, reported by Johnson & Johnson last month, indicated that a booster can indeed improve protection. In November 2020, the company launched 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, efficacy rose to 94 percent. Globally, the increase was more modest, at 75 percent — about the same efficacy reported for a single dose in the US during the winter. Against severe to critical Covid-19, two shots had 100 percent efficacy.
Noah Weiland contributed reporting from Washington, DC; Amy Schoenfeld Walker from Trumbull, Conn.; and Carl Zimmer van Guilford, Conn.