The study, which was published as a preprint before peer review, is an early proof of concept that the approach may work, but the vaccine formula is not likely to ever be used. Moderna’s lead booster candidate, which is tuned to block the omicron variant and the original version of the virus, is still in human testing, with results expected by the end of June.
While the bivalent shot that was the subject of Tuesday’s report includes four of the mutations found in the omicron variant, the omicron bivalent vaccine will include 32 of those mutations.
Outside experts noted that the research provided limited insight into the future vaccination strategy because this vaccine formulation isn’t likely to be used. The beta variant emerged in South Africa in late 2020 and raised alarm because of its ability to bypass immunity, but it quickly fizzled out. Experts are closely watching as omicron evolves into new subvariants around the world.
“At this point, we should at least be thinking about a bivalent Omicron booster,” David R. Martinez, a viral immunologist at the University of North Carolina Gillings School of Global Public Health, said in an email. “We should also be asking ourselves what the overall goal is, as the variant-specific boosters are a patch-fix approach, and the ancestral vaccines seem to be doing a generally good job at protecting against severe disease.”
The increase in immune defenses in the study were measured in laboratory tests. The twofold boost in antibodies that block omicron “may be statistically significant but are unlikely to be biologically important,” John P. Moore, a professor of microbiology and immunology at Weill Cornell Medicine, wrote in an email.
An expert committee that advises the Food and Drug Administration met this month to debate the possible composition of a booster vaccine in the fall but did not review specific data. The committee is expected to agree again in coming months to help select the best vaccine for a potential fall booster campaign.
The beta bivalent shot appeared to broaden immunity, triggering higher levels of antibodies, “even when additional variants of concern were not included in the booster vaccine,” Stéphane Bancel, Moderna’s chief executive, said in a statement. “We believe that a bivalent booster vaccine, if authorized, would create a new tool as we continue to respond to emerging variants.”
Antibody levels were higher with the bivalent vaccine compared with a regular booster against a range of variants and remained so after six months, with the exception of the delta variant. The study was not designed to measure vaccine effectiveness.