New COVID-19 boosters are coming this fall, the FDA announced late last month in the wake of an expert advisory committee meeting that considered the makeup of future vaccines.

The expert committee struggled with incomplete data and the impossibility of predicting the pandemic’s trajectory, but ultimately came down on the side of new “bivalent” boosters encoding both the original coronavirus spike and a spike representing the latest versions of the omicron variant, BA.4 and BA.5, which together are now dominant in the United States. The spike proteins of BA.4 and BA.5 are identical, so only one additional component is necessary to update vaccines for both.

Vaccine-makers presented their latest data on booster formulas for different variants, but the results did little to clarify the situation for the committee.

Pfizer reported that its booster targeting BA.1, an earlier omicron variant, led to more anti-omicron antibodies than the original vaccine. The booster encoding only the omicron spike was more effective than a bivalent shot that also included the original spike mRNA.

In contrast, Moderna advocated a bivalent approach, which the company’s president Dr. Stephen Hoge said resulted in longer-lasting antibodies compared to single-spike formulas.

Amid those apples-and-oranges results, Novavax then tossed in a pineapple. Novavax’s Dr. Gregory Glenn argued that no update is necessary for its protein-based vaccine to combat the latest omicron variants. A booster of the company’s original formula, Glenn said, resulted in anti-BA.5 antibodies at levels comparable to the antibodies it produced against the original strain. Novavax is still awaiting emergency authorization of its two-dose primary series.

Some experts said they were impressed with Novavax’s findings, but the committee finally voted 19-2 in favor of changing the formulas for boosters to include an omicron variant.

Pediatrician Dr. Paul Offit, one of the two dissenters, co-authored a STAT opinion piece with immunologist John P. Moore in which the pair expressed concern about rushing the decision on updated boosters without complete data. They noted that omicron-specific booster shots from Pfizer and Moderna increase the amount of neutralizing antibodies against omicron by twofold or less. It’s not clear if that will translate to significantly enhanced real-world protection against infection or disease.

At the FDA advisory committee meeting, virologist Kanta Subbarao presented the World Health Organization’s preference for vaccines containing the BA.1 omicron variant, citing its status as the variant that’s most evolutionarily distinct, so far, from the original virus from Wuhan, China. The hope is that a booster based on the original and omicron BA.1 strains together could create immunity against the broadest spectrum of possible future variants.

But the FDA’s Dr. Peter Marks has opined that any new vaccine should target the most recent versions of the virus in circulation, which would be BA.4 and BA.5. These variants are also quite distant, evolutionarily speaking, from the original coronavirus. Several committee members endorsed this approach.

Vaccine-makers said they could have bivalent shots with the BA.4/5 spike ready by fall, assuming regulators approve them speedily. The FDA will not require clinical trial data to authorize the vaccines, reports Michael Erman at Reuters. The primary series of vaccinations with Pfizer and Moderna mRNA vaccines will remain the same, reports Noah Weiland at The New York Times.

Leave a comment

Your email address will not be published.