People who have received Pfizer-BioNTech vaccines may benefit just as much from a Johnson & Johnson booster injection as they did from a Pfizer vaccination. That’s the finding of a small study released Sunday.
Researchers at the Beth Israel Deaconess Medical Center in Boston studied 65 people who had received two injections of the Pfizer vaccine. Six months after the second dose, the researchers gave 24 of the volunteers a third dose of the Pfizer vaccine and 41 gave the Johnson & Johnson injection. (The study was funded in part by Johnson & Johnson and has not yet been published in a scientific journal.)
Both vaccine brands increased the number of Covid-fighting T cells, which are important for long-term protection and to prevent infections from turning into serious diseases. But the increase in T cells delivered by the Johnson & Johnson vaccine was twice that of Pfizer.
The researchers also measured antibodies, which provide a large part of the protection immediately after vaccination. Volunteers who received a third dose of Pfizer saw their antibody levels rise after two weeks and then decrease by a quarter by the fourth week. The Johnson & Johnson booster, on the other hand, more than doubled antibody levels between the second and fourth weeks. At that time, Pfizer’s antibodies were still about 50 percent higher than Johnson & Johnson’s. For antibodies this is a relatively small difference. And both levels were well above the threshold scientists say is necessary for strong protection.
The results differ slightly from previous studies. In October, a “mix and match” clinical trial organized by the National Institutes of Health reported that all three authorized vaccines — from Pfizer, Moderna and Johnson & Johnson — caused antibody levels to rise when used as a booster. But Johnson & Johnson’s shot gave a much smaller boost than the others. (The NIH has not yet published how each booster affected the volunteers’ T cells.)
The difference between the two studies can be explained by the length of the delay between the shots. In the NIH study, many of the volunteers received their booster injections after three or four months, while the new study waited six months.
The Johnson & Johnson vaccine seems to have benefited more from the longer wait. Unlike Pfizer and Moderna, which are made from mRNA, Johnson & Johnson’s is made from a modified cold virus. It may be important to give the immune system more time to return to a resting state before receiving this type of vaccine.