An advisory panel to the U.S. Food and Drug Administration voted unanimously on Thursday to recommend that COVID booster shots be updated for the fall to protect solely against one of the three XBB variants that have taken hold in the United States.

Those three XBB variants, which are all sublineages of the Omicron variant, are XBB.1.5, XBB.1.16 and XBB.2.3, CNN reported. What will be dropped from the updated vaccines will be protection against the original strain of the virus because experts believe it could contribute to lower vaccine efficacy against newer strains.

“Your immune response likes to react to what it’s seen before,” Dr. David Ho, a professor of microbiology and immunology at Columbia University whose research was cited in FDA briefing documents, told CNN.

“That’s why we made the recommendation that if you want to broaden out your antibody responses, it’s best to remove the ancestral spike in future vaccines,” Ho explained.

Although the FDA will make the final decision on the updated vaccines, it typically follows the advice of its advisory panels.

While infections have declined across the United States, the virus could be a concern next winter, the FDA’s vaccine chief Dr. Peter Marks said as the daylong meeting began, the Associated Press reported.

“We’re concerned that we may have another wave of COVID-19 during a time when the virus has further evolved, immunity of the population has waned further, and we move indoors for wintertime,” he told the panel, the AP reported.

A big question will be who should get the updated boosters, Dr. Paul Offit, a vaccine scientist at the Children’s Hospital of Philadelphia and a member of the advisory committee, told CNN before Thursday’s meeting.

“What’s the goal of the vaccine?” he asked. “If the goal of the vaccine is the stated goal, which is protection against severe disease, do you really need a yearly vaccine for otherwise healthy people less than 75? I mean, is this the flu model? Because I would argue it shouldn’t be.”

It’s important to have evidence about whether protection from the COVID vaccine against hospitalization and death is waning and, if so, in which groups, he added.

In a presentation at the advisory panel meeting, the U.S. Centers for Disease Control and Prevention said there is evidence of waning protection from bivalent boosters against hospitalization, CNN reported.

COVID-19 boosters will likely be offered this fall, once they are redesigned by vaccine makers.

FDA scientists believe redesigned boosters should target at least one variant of XBB, according to briefing documents published Monday.

“These data suggest that an updated strain composition of COVID-19 vaccines to more closely match currently circulating Omicron sublineages is warranted for the 2023-2024 vaccination campaign,” the scientists wrote.

The World Health Organization and the European Medicines Agency have both already said that a booster should target an XBB subvariant.

As the virus has changed, vaccines have evolved, from a shot in December 2020 that targeted the original virus to FDA-approved shots last fall that targeted the original COVID strain as well as the Omicron subvariants BA.4 and BA.5.

XBB 1.5 is the dominant strain now circulating, with 40% of new cases having this strain, according to the CDC. About 18% of new cases have XBB.1.16 and 12.5% have XBB 1.9.1.

Current boosters provide some protection against XBB 1.5, but not as much as for BA.4 and BA.5.

The FDA’s Advisory Committee on Immunization Practices, which will decide who should get a booster, will also meet next week to talk about this and other vaccines.

It would make sense if the COVID boosters were offered to everyone in the fall, Dr. Ofer Levy, director of the Precision Vaccines Program at Boston Children’s Hospital, told NBC News.

“In my mind, it seems like a logical framework,” said Levy, a member of the FDA’s advisory committee. “It will boost your antibody response and it probably affects your T-cells as well, in a positive way.”

More information

The World Health Organization has more on COVID-19.

SOURCE: CNN; Associated Press; NBC News