On Tuesday, a panel of experts will advise FDA on whether an updated vaccine should target a version of the omicron variant—a move that would have federal regulators decide exactly which formulation to use this fall.

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FDA considers updating Covid-19 vaccines for fall

FDA is considering whether an updated vaccine aimed at boosting people's immunity ahead of a likely winter surge is necessary, the New York Times reports.

Federal health officials may push to release a bivalent vaccine that targets the BA.4 and BA.5 omicron subvariants, which make up more than one-third of U.S. cases and could be more similar to the version of the virus circulating this fall.

However, if the agency decides to authorize an updated version of the Covid-19 vaccine based on omicron subvariants this fall, it may need to forgo human trials in favor of an expedited process that more heavily relies on laboratory tests and animal trials.

According to Kelly Moore, president of Immunize.org, a nonprofit group that works to increase immunization rates, this type of accelerated process is already used to update the annual flu vaccine.

While this would be the United States' first attempt at creating the next generation of Covid-19 vaccines, Moore noted that the existing shots have already been safely administered to hundreds of millions of people. According to Moore, updating them might call for "very well-educated guesswork," but, she said these kinds of deductions are "appropriate for the circumstances."

Ultimately, if the government decides to move forward with a booster shot that targets the BA.4 and BA.5 omicron subvariants, there will still be a race to produce adequate doses by fall—even with accelerated testing.

Scientists have also highlighted the possibility that the virus could evolve again, rendering an updated omicron vaccine ineffective.

"Do we target BA.4 and 5? They will probably peak somewhere in the next month or two," said John Beigel, a clinical research director at the NIH who has conducted multiple coronavirus vaccine studies. "They may be old news by the time the fall comes."

According to Beigel, an alternative option is to keep using the existing vaccines, which still provide adequate protection against severe illness, but very little against infection.

The advisory panel will likely split between those who would broadly support fall booster shots and those who would limit additional shots to high-risk individuals, the Times reports.

Vaccine makers release data on omicron-specific boosters

Earlier this month, Moderna released preliminary data on its omicron-specific booster—a bivalent vaccine called mRNA1273.214.

The clinical trial involved 814 volunteers with an average age of 57 vaccinated with three doses of Moderna's existing vaccine. Of the volunteers who had no signs of prior coronavirus infection, the researchers found that their new vaccine combination resulted in a 6.3-fold increase in neutralizing antibodies against BA.4 and BA.5. Among all participants, there was a 5.4-fold increase in neutralizing antibodies.

Although the levels of neutralizing antibodies against the newer omicron subvariants were lower than those against the original omicron variant, they were still high overall, Moderna said.

"In the face of SARS-CoV-2's continued evolution, we are very encouraged that mRNA-1273.214, our lead booster candidate for the fall, has shown high neutralizing titers against the BA.4 and BA.5 subvariants, which represent an emergent threat to global public health," said Moderna CEO Stéphane Bancel.

In a separate clinical trial, Pfizer and BioNTech tested a vaccine candidate that targets the spike protein of the omicron BA.1 variant, and a "bivalent" vaccine candidate that combined its omicron-modified vaccine with its vaccine for the original strain of Covid-19.

On Saturday, the companies announced that a trial of two of its omicron-modified Covid-19 vaccines produced a "substantially higher immune response" against omicron BA.1 when compared with the companies' current Covid-19 vaccine.

When given as a fourth booster dose, the omicron-modified candidate increased participants' neutralizing antibodies between 13.5 times and 19.6 times.

Similarly, Pfizer's "bivalent" vaccine candidate increased neutralizing antibodies between 9.1 times and 10.9 times against the omicron variant.

Because preliminary studies have demonstrated that both omicron-adapted candidates are less effective at neutralizing BA.4 and BA.5 than BA.1, BioNTech CEO and co-founder Ugur Sahin said the companies will "remain vigilant" and "are prepared to rapidly adapt [their] Omicron-adapted vaccine candidates to emerging sublineages if epidemiological and laboratory data suggest."

"As we've said since the early days of the pandemic, we will follow the science and adapt our own approaches as needed to help address COVID-19 as the virus evolves," said Pfizer CEO Albert Bourla. "We believe we have two very strong Omicron-adapted candidates that elicit a substantially higher immune response against Omicron than we've seen to date." (LaFraniere, New York Times, 6/27; AP/NPR, 6/25; Reed, Axios, 6/25; Herper, STAT News, 6/25)