The researchers found that those who got a Johnson & Johnson shot followed by a Moderna booster saw their antibody levels rise 76-fold within 15 days, whereas those who received another dose of Johnson & Johnson saw only a fourfold rise in the same period. A Pfizer-BioNTech booster shot raised antibody levels in Johnson & Johnson recipients 35-fold.
The authors cautioned about the study’s small size and noted that they did not follow the volunteers long enough to identify rare side effects.
Scott Hensley, an immunologist at the University of Pennsylvania who was not involved in the new study, found the results compelling. He noted, however, that the trial only looked at antibody levels, which on their own are an insufficient measure of how well different combinations of vaccines would lower Covid-19 infections and hospitalizations.
“At the end of the day, folks having the Johnson & Johnson should probably get an mRNA booster,” he said. “It’s just a matter of, how much data does the F.D.A. need before making that recommendation?”
“I wouldn’t want to be in their shoes,” he added.
Some scientists question how the federal government is considering boosters of any brand, given the limited data provided not only by Johnson & Johnson, but the other companies as well.
“There are some of us who would really like to see more data,” said Dr. Celine Gounder, an infectious disease specialist at Bellevue Hospital Center in New York. “And then there are others who want to just move forward on boosters.”