Will the New COVID-19 Vaccine Work Against the BA.2.86 Variant?

COVID-19 isn’t quite done with the world yet. Small surges of cases in the U.S., as well as upticks in COVID-19 hospitalizations over the summer, and new variants that weren’t around even three months ago, remind us that SARS-CoV-2 is still a health threat for the coming fall and winter.

The U.S. Food and Drug Administration (FDA) is expected to make a decision about which strain to target in the updated vaccine, which the agency says will be available in mid-to-late September. The FDA will be considering recommendations by the panel of independent vaccine experts it convened in June, which reviewed the latest data on an updated COVID-19 vaccine and which strains would likely be circulating in the fall and winter. The 21-member panel voted unanimously to update the next COVID-19 vaccine, and recommended moving from the current bivalent shot that targets two Omicron variants, BA.4 and BA.5, to now include a single XBB strain. The agency is still deciding which specific XBB strain the new vaccine will incorporate, although at the time, the dominant strain causing new infections was XBB.1.5.

As of the middle of August, however, new variants have emerged, and XBB.1.5 now accounts for around 5% to 6% of infections in the U.S. Omicron variant EG.5, a new evolution of XBB, is now the dominant variant, contributing to 20% of COVID-19 infections in the country, followed by Omicron FL.1.5.1, which accounts for 13% of cases. And two cases of BA.2.86, a descendant of XBB.1.5, have recently been reported in the U.S. It contains dozens of mutations that researchers are studying to understand whether the variant could potentially spread faster or cause more severe disease.

Based on the June recommendation, vaccine makers have been manufacturing updated vaccines that target XBB, in order to ensure enough doses are ready by the fall and winter season. How well do these vaccines work against the newer variants?

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In August, Moderna reported that its XBB-based vaccine can neutralize the newer EG.5 and FL.1.5.1 variants as well as XBB. The results were based on early findings from a study the company conducted to test its vaccine in a small group of people.

Pfizer said in a statement to TIME that in a study in mice, its XBB vaccine “effectively neutralized a number of Omicron XBB variants, including XBB.1.5 and EG.5.1.”

Novavax similarly reported that its XBB-targeted vaccine generated neutralizing antibodies against EG.5.1, but its studies were also limited to animals. The company’s vaccine uses a different technology from Moderna that relies on including viral proteins in the vaccine to stimulate the immune system, and takes slightly longer to manufacture. Moderna and Pfizer’s vaccine use genetic material from the virus, in the form of mRNA, to activate an immune response—this technology makes it possible to generate new vaccines in about six weeks, shorter than Novavax’s approach takes.

In any case, all those early findings are good news for the upcoming COVID-19 season—so far. Because the newer variants dominating U.S. cases are still part of the Omicron family, the vaccines made to target XBB may still be effective against them because the shots focus on portions of the virus that remain the same among these different versions.

How dangerous is the BA.2.86 variant?

But it's not clear how long that luck will continue to hold. Some experts are already raising alarms about BA.2.86, which has contributed to only a handful of cases worldwide so far. But it contains more than three dozen new mutations compared to XBB.1.5, based on nine viral genomes that researchers have analyzed so far, and therefore represents an evolutionary jump from existing strains that could make it a threat to public health. So far, only two cases of the new variant have been reported in the U.S., but there have been cases in a number of other countries, including Denmark, South Africa, Israel, and the U.K.

The U.S. Centers for Disease Control and Prevention (CDC) issued a statement on Aug. 23 summarizing what’s known so far about the variant, which isn’t much. So far, current tests and treatments, including antiviral drugs, are effective against BA.2.86. But early data suggest that this strain may be more likely to infect people who have been vaccinated or have had previous infections than previous strains. Still, “[a]t this point, there is no evidence that this variant is causing more severe illness,” the agency said, and “CDC’s current assessment is that [the] updated vaccine will be effective at reducing severe disease and hospitalization.”

CDC director Dr. Mandy Cohen recently told TIME she is not concerned about the current level of COVID-19 hospitalizations from COVID-19. But, she added, “we’re going to continue to watch that. We have to keep vigilant and make sure that we’re using the tools [we have] to protect ourselves.” There’s no certainty yet whether BA.2.86 will continue to increase, whether it will lead to a spike in hospitalizations, or whether the XBB vaccines will be able to generate a strong enough immune response to protect against infection. The World Health Organization has classified BA.2.86 as a “variant under monitoring,” and the CDC will continue to track the variant through systems such as genomic testing of travelers coming to the U.S. and sampling and sequencing of wastewater samples throughout the country.