Given the ability of the Omicron variant to evolve, Dr. Burton said, “I think we have to just assume it is going to be major player, still, in the fall.”
Moderna’s researchers measured levels of antibodies — the body’s first line of defense in warding off infection from the coronavirus. Other immune responses that also defend against Covid-19 disease were not measured; those tests are far more complex and time-consuming to conduct.
Dr. Paul A. Offit, a vaccine expert at Children’s Hospital of Philadelphia, said the failure to analyze the strength of memory B cells and T cells, which are a powerfully protective part of the immune system’s response, is the Achilles’ heel of studies like Moderna’s. At a recent meeting of the Food and Drug Administration’s vaccine advisory board, of which he is a member, Dr. Offit asked an expert with the National Institutes of Health whether such research was underway.
The expert, Dr. John Beigel, who is directing studies similar to Moderna’s, described such data as critical. In a recent interview, though, he said that while antibody levels provide only a partial picture of the immune system’s response, “keeping antibody levels high is important.” He said that at least to some degree, those levels reflect broader immunity.
Dr. Jesse L. Goodman, a former chief scientist at the F.D.A., said Moderna’s results were promising, but did not conclusively prove that a bivalent vaccine would be better than existing ones.
He said the control group that received Moderna’s existing booster was drawn from a different study, so there was not a direct, head-to-head comparison between those volunteers and the ones who got the bivalent vaccine. For example, the volunteers were not all given a booster shot at the same time after their second shot, which he said could affect the results. “That is a significant uncertainty in the study,” he said.
The sprint to update the vaccines involves small clinical trials paired with laboratory tests. First, vaccines are designed to target a variant — either alone or in combination with the original prototype of the virus or another variant.
