As the BA.4 and BA.5 subvariants of omicron dominate Covid-19 cases in the United States, FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) on Tuesday voted to recommend the use of a Covid-19 booster shot specifically crafted to target the omicron variant in the fall.

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Omicron subvariants dominate Covid-19 cases in the US

According to new estimates released Tuesday by CDC, BA.4 and BA.5 are now the dominant strains in new coronavirus cases.

As of the week ending June 25, BA.4 comprised 15.7% of all new coronavirus cases, and BA.5 comprised 36.6% of new cases, representing around 52% of all new coronavirus cases in the United States combined, according to CDC.

And while Covid-19 hospitalizations in the United States were up 6% over the last two weeks, as of Monday, with an average of 31,000 hospitalizations each day, new Covid-19 deaths have remained below 400 per day on average, federal data shows.

"What we're seeing is that the average case of Covid-19 is becoming much milder," said David Dowdy, an epidemiologist at Johns Hopkins Bloomberg School of Public Health.

"This wave feels qualitatively and quantitatively different," said Megan Ranney, an emergency physician at Brown University. "We're not seeing our I.C.U. get filled up with patients who are gasping for breath or who are on death's door."

"Overall, the people who've been coming through with Covid are much, much less sick than they were even this winter," she added. "It feels like almost a different disease for folks, with the exception of people who are really old, who are unvaccinated or who are immunosuppressed."

"But in my mind, 250 deaths a day is still too many," said CDC Director Rochelle Walensky.

VRBPAC recommends updating booster shots for the fall

Meanwhile, VRBPAC on Tuesday voted 19-2 to recommend updating Covid-19 booster shots to target omicron this fall, specifically recommending the shot target BA.4 and BA.5 rather than the original omicron variant.

During the meeting, Pfizer and Moderna presented data showing that updated vaccines were able to produce moderately higher levels of antibodies; however, it's still unknown whether that will cause improved protection against hospitalization or infection. In addition, both target the original omicron variant, and preliminary studies have demonstrated that both omicron-adapted candidates are less effective at neutralizing BA.4 and BA.5 than BA.1.

Some members of the panel emphasized that waiting much longer to start producing and authorizing a new booster shot could mean the shot isn't available in time. Both Moderna and Pfizer have said that developing a booster shot targeting BA.4 and BA.5 rather than BA.1 will delay their delivery times. Moderna said it could have a shot ready by late October while Pfizer said it could have one ready by the first week of October.

"I think given the speed of evolution [of the virus] we're going to be behind the eight ball if we wait longer," said Mark Sawyer, a professor of clinical pediatrics at the University of California San Diego School of Medicine. "Public perception is that FDA is already delaying approvals. I think we have enough data here presented today to move forward with a strain change."

However, while Paul Offit, professor of pediatrics at Children's Hospital of Philadelphia, voted against the recommendation, he agreed that "we need to broaden the immune response" of the booster shots. He added that it's unclear whether omicron is the correct strain to use, calling the data "uncomfortably scant."

"I'm still not comfortable enough that we have the information we need to essentially support this new product, and I don't think it's fair to ask people to take a risk if we don't feel comfortable with the level of protection we're likely to get," he said.

Experts on the panel also debated whether the updated booster should be monovalent, meaning it only contains an omicron strain, or bivalent, meaning it contains the original vaccine strain in addition to an omicron strain.

A number of experts have said they favor a bivalent vaccine because it combines the proven success of the original vaccine with some cross-protection against new variants.

"I'm a fan of bivalent vaccines because the original vaccine has done so well," said Stanley Perlman, a professor of pediatrics at the University of Iowa. "There are multiple anecdotal and other discussions of how people are getting infected with BA.4/5 after having been infected with BA.1, so the protection of BA.1 is not so great, so that's what puts me more toward a BA.4/5-containing vaccine."

Ultimately, FDA will have to decide the exact vaccine recipe. And according to Peter Marks, director of FDA's Center for Biologics Evaluation and Research, the agency's goal is to make a strain composition recommendation by early July so companies have enough time to manufacture doses for a booster campaign in October.

Marks said that by adjusting the booster shots this fall, "we're hoping we can convince people to go get that booster to strengthen their immune response and help prevent another wave." (Gardner, Politico, 6/28; Neergaard/Perrone, Associated Press, 6/28; Johnson/Shepherd, Washington Post, 6/28; Bettelheim/Reed, Axios, 6/29; Frieden, MedPage Today, 6/29; Hassan, New York Times, 6/28; Mueller, New York Times, 6/20)