New COVID variant XBB.1.5 is on track to become dominant in the US, and experts are worried

The new subvariant is the most transmissible, Maria Van Kerkhove, technical lead for the World Health Organization’s COVID-19 response, said at a news conference on Wednesday. So far, however, there is no evidence that the new strain causes disease more severely than other Omicron variants.

Currently, WHO’s main concern with the variant is its ability to spread easily compared to other Omicron strains, officials said. XBB.1.5 is “rapidly replacing other variants” in some European countries and the Northeast US, where it accounts for most infections, according to Van Kerkhove.

As of Friday, XBB.1.5 was responsible for an estimated 75% of cases in the US Centers for Disease Control and Prevention regions 1 and 2, which include Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont, New York, New Jersey, Puerto Rico, and the US Virgin Islands, according to the federal health agency.

And it is projected to be responsible for more than 40% of the country’s consecutive COVID cases, putting it on track for potential dominance when the agency updates its projections on Friday.

“In recent weeks there have been increasing reports of hospitalizations and pressure on the health system, especially in the temperate regions of the Northern Hemisphere, where respiratory diseases, including influenza, are also circulating,” said WHO Director-General Tedros Adhanom Ghebreyesus on Wednesday.

The Northeast US—where XBB.1.5 is responsible for most consecutive cases of COVID—has seen an increase in hospitalizations, Van Kerkhove said.

But it’s too early to conclude whether the new variant is responsible for the increase, he said. Other respiratory viruses, such as RSV and influenza, are also circulating in the area, and an increase in COVID cases is expected after the holiday, regardless of the new variant that appears, he added.

Due to the spread of XBB.1.5 in the US, the WHO asked the CDC to report the risks of the new variant. The WHO’s own technical advisory group on the evolution of the virus is also working on a risk assessment, which is expected to be released in the coming days.

The XBB.1.5, first identified in October, is a combination of two spinoffs of the BA.2, “stealth Omicron.” In addition to the US, levels of the new variant are rising rapidly in Europe, WHO officials said. Currently, it is known in more than 25 countries.

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