The second study showed that the J&J vaccine’s immune response lasted at least eight months and that some types of immune cells increased over time. This immune response was found to provide protection even against the delta variant and other variants of concern.
This builds onto research from J&J’s clinical trial before its vaccine received authorization from the FDA. In that study, the vaccine was found to be 72% effective at preventing severe and moderate disease in the U.S. Part of the trial was also conducted in South Africa and Brazil, where variants were circulating as the vaccine was being tested. Those results were slightly lower than in the U.S. trials — 57% in South Africa and 66% in Latin American nations — but, overall, those percentages confirm a high degree of protection.
Still, those percentages were lower than what Pfizer-BioNTech and Moderna had reported in their trials — 95% and 94% effectiveness, respectively, at preventing symptomatic disease. Recent data suggests the two vaccines also protect against the delta variant.
That means that, while there is now some evidence that J&J is protective against the delta variant, its overall efficacy is still lower than that of Pfizer-BioNTech or Moderna, said John Moore, a professor of microbiology and immunology at the Weill Cornell Medical College in New York.
“I don’t think anything has changed about that,” said Moore. He had previously told KHN he thought J&J should be a two-dose vaccine, since it provides less protection than Pfizer and Moderna.
He also pointed out that, if you look closely at one of the new J&J studies, a single person did elect to get an mRNA dose after receiving J&J, which strongly boosted that person’s antibody response.
“That is just a one-off result,” said Moore. “But it is consistent with emerging data.”
Indeed, data from studies in the United Kingdom shows that following a single dose of the Oxford-AstraZeneca shot with a Pfizer-BioNTech shot offered an immunity boost. (The Oxford-AstraZeneca vaccine, authorized for use in the U.K. but not the U.S., operates through a similar mechanism as J&J, although two doses are required.)
Experts, though, also maintain that all the covid vaccines authorized for emergency use in the U.S. are very effective, especially compared with other types of vaccines. Flu vaccines have been found to have an average of 33% to 61% effectiveness, depending on the strain they protect against.
Still, Moore said those who got J&J should not pursue booster shots on their own but instead wait for guidance from the Centers for Disease Control and Prevention and FDA.