FDA Panel Recommends New Monovalent COVID Booster Targeting XBB Variant

Vaccine makers should formulate the newest COVID-19 booster to protect against the XBB variant, an advisory panel to the Food and Drug Administration voted Thursday.

The unanimous decision from the Vaccines and Related Biological Products Advisory Committee indicates a preference for moving the U.S. away from the current bivalent boosters—which target earlier strains of the virus—and instead aiming it at the dominant variant in circulation right now.

“The original strain of the virus is now virtually gone from around the world,” William Schaffner, MD, professor of infectious disease at Vanderbilt University, told Health. “The thinking is that it’s best to focus on the variants that are currently circulating and causing the most illness.”

The FDA will now review the advisory committee’s recommendation to make a decision about how to formulate the fall boosters. The committee’s recommendations are not binding, but the FDA typically follows its recommendations.

XBB was first detected in the U.S. last fall, and has since grown to become the dominant variant. The Centers for Disease Control and Prevention (CDC) has been tracking at least nine different subcategories of the strain—including XBB.1.5—which together account for an estimated 99% of COVID cases for the week of June 10.

The advisory committee also discussed which specific strain of XBB should be included in the updated shot, though it’s not making an official decision at the time. Members said that the early data showed little difference between the specific subvariants such as XBB.1.5 or XBB.1.16, so the decision will likely come down to which shots are easiest to manufacture.

It’s also not yet clear when the new monovalent boosters would be available to the public, though it will likely be sometime in September, Peter Marks, PhD, MD, director of the FDA’s Center for Biologics Evaluation and Research, said during Thursday’s meeting.

Why Does the COVID Vaccine Keep Changing? 

Though COVID is no longer a public health emergency, it’s still important that researchers track the virus and update the tools we have to fight it.

Protection from COVID vaccines wanes over time. And it may decline quite dramatically—a new review found that nine months after someone received a booster dose, the vaccine efficacy against Omicron infection and symptoms was lower than 30%.

Getting re-vaccinated against the most commonly circulating variant or variants should give someone good protection against a severe COVID infection for at least six to eight months, said Dr. Schaffner. Data shows that prior infection with non-XBB variants or previous vaccination may not be able to protect someone from getting an XBB.1.5 or related infection.

“We have to follow the virus. If the virus remains pretty stable, then you don’t have to change the vaccine. For example, with flu, you don’t change every element in the vaccine each year,” Dr. Schaffner said. “Of course, we follow the [flu] virus, we do surveillance of the virus to make that determination. We will do something very similar with COVID.”

If virus mutations remain minor, the vaccine may not even need to be updated in the future, he added. But there’s no way of knowing, for now.

As for the current proposed vaccine update, the move from a bivalent to a monovalent vaccine is yet another way to hopefully improve protection against the currently circulating COVID strains.

In the FDA’s briefing documents for the meeting, it highlighted the issue of “immune imprinting,” the idea that the immune system’s memory of older variants could hinder the body’s ability to respond to new variants. Research from a preprint study has suggested that removing this original COVID strain from the vaccines would make protection for the newer variants stronger.

Plus, Dr. Schaffner added, trying to create a COVID shot that addressed every current and former circulating variant would get logistically complicated. Pursuing a monovalent option “[makes] the vaccine as simple as possible to provide the broadest coverage, so that it can be made quickly,” he said.

Vaccine Hurdles Remain 

An updated COVID shot is certainly good news if it serves to bolster people’s immunity to COVID. About half of adults say they would likely get an annual COVID shot, according to KFF, yet only 17% of those who are eligible have gotten a bivalent booster.

“As a friend of mine likes to say, ‘Vaccines don’t prevent disease. Vaccination prevents disease,’” Dr. Schaffner said. “The acceptance of an updated booster will be very interesting this fall.”

In addition to persistent vaccine hesitancy, the logistics of convincing people to get vaccinated this fall may be difficult, he explained. Not only will most people have to get both a flu and a COVID shot in the fall, but some people—likely seniors—may also be eligible for a respiratory syncytial virus (RSV) vaccine. Asking people to get three shots may be a lot.

It’s also true that COVID hospitalizations and deaths are steadily declining, even in light of concerns about waning immunity. People may not feel like it’s necessary to keep getting COVID or other shots.

“That will be a challenge for all of us in public health, infectious diseases, and just general medicine,” Dr. Schaffner said. “We have a large task facing us this fall if we wish to do a comprehensive immunization with all the recommended vaccines for our population.”