An Omicron subvariant that’s starting to gain global attention is XBB, which comes from the BA.2 sublineage of the COVID virus.

How did XBB come to be? Andy Pekosz, PhD, a virologist and the vice-chair of the Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health, told Verywell that since XBB is a combination of the BA.2.10.1 and BA.2.75 sublineages, it means the subvariant has parts of two different viruses that infected the same host and exchanged some of their genes in the process.

But there’s no need to panic. According to the World Health Organization’s (WHO) Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE), XBB is considered part of the Omicron variant. The group concluded that XBB and its sublineages don’t need a new label or to be designated as a new variant of concern because they’re not very different from other Omicron sublineages.

Where XBB Has Spread

As of October 2022, XBB has been detected in 35 countries, including the United States. The subvariant recently drove a surge of COVID cases in Singapore and has been responsible for many cases in India, Australia, and South Korea as well.

Spread in the U.S.

It’s too soon to tell if XBB will cause a surge in the U.S. However, Raj Rajnarayanan, PhD, assistant dean of research and associate professor at the New York Institute of Technology College of Osteopathic Medicine’s Arkansas State University campus, tweeted that New York is an emerging hotspot for the spread of XBB and its sublineages.

Pekosz said we don’t know how well XBB will compete with current Omicron variants in the U.S. But we do know that other subvariants like BQ.1.1, BF.7, and BA.2.75.2 have similar mutations, and they are increasing in the U.S. Therefore, he said XBB is worth watching carefully.

Whether XBB will cause an uptick in infections could depend somewhat on a region’s immune landscape, which includes factors like COVID vaccination coverage and the size and timing of previous waves of Omicron.

Is XBB More Contagious or Severe?

Pekosz pointed out that COVID cases are increasing in a highly vaccinated population in Singapore, which suggests XBB might be more transmissible.

For example, mutations have changed the spike protein of the COVID virus. As a result, vaccines and treatments have had to adjust, too.

Risk of Reinfection

Diana Finkel, DO, an assistant professor in the Department of Medicine and director of the Infectious Disease Fellowship Program at Rutgers New Jersey Medical School, told Verywell that compared to other Omicron sublineages circulating, early evidence suggests there might be a higher reinfection risk with XBB. In other words, even if you already had COVID, it’s possible you could get reinfected with the XBB variant.

People who were reinfected with XBB initially got COVID before the Omicron period. However, we need to see more data to know for sure whether XBB escapes Omicron immunity or not.

Finkel said that while there’s no evidence yet that XBB will pose a greater risk than other Omicron subvariants, we still need to be on the lookout and keep an eye on the rate of new infections.

Is XBB More Severe?

Right now, there are no signs that XBB causes more severe COVID illness. However, people should keep in mind that there are many factors that influence how sick a person will get if they catch COVID, not just which variant they get.

Will Vaccines and Treatments Work Against XBB?

Pekosz said that even though Singapore saw a large number of COVID cases, there wasn’t a big spike in hospitalizations. This could suggest that COVID vaccines can still offer protection against severe disease—about 92% of Singapore’s population is fully vaccinated and 80% have had their booster shots.

Still, it appears that the recombinant XBB.1 is more resistant to the neutralizing antibodies induced by booster doses than other circulating subvariants like BA.4/5, BQ.1.1, and BA.2.75.2.

Early data shows that the immune response induced by a bivalent COVID booster was enhanced in people who already had COVID. However, the findings are based on preliminary evidence, and more studies are needed.

The medications we currently have to treat COVID are expected to still be effective against the circulating variants and XBB. However, Finkel said that Evusheld (a combination of monoclonal antibodies tixagevimab and cilgavimab) might not work as well.

In a preprint study published to medRxiv, researchers said that XBB is one of the most antibody-evasive mutations they’ve tested and that it shows strong resistance to antibody drugs. Those convergent mutations of Omicron may evade neutralizing antibody (NAb) drugs (like Evusheld and Bebtelovimab) and convalescent plasma.

Health agencies worldwide are closely watching the XBB variant and trying to learn as much as they can about it.

For now, the best step you can take to protect yourself from COVID is to get a bivalent booster when you’re eligible. The updated shots provide better protection against the Omicron variant than the previous monovalent booster vaccines.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

For now, the best way to protect yourself against COVID is still getting vaccinated and boosted.