Highly immune evasive omicron XBB.1.5 variant is quickly becoming dominant in U.S. as it doubles weekly

Key Points

• The Covid omicron XBB.1.5 variant has nearly doubled in prevalence over the past week and now represents about 41% of new cases in the U.S., according to CDC data.

• XBB.1.5 is highly immune evasive and appears to bind better to cells than other members of the XBB omicron subvariant family.

• Scientists at Columbia University have warned that the rise of subvariants such as the XBB family could “result in a surge of breakthrough infections as well as re-infections.”

The Covid omicron XBB.1.5 variant is rapidly becoming dominant in the U.S. because it is highly immune evasive and appears more effective at binding to cells than related subvariants, scientists say.

XBB.1.5 now represents about 41% of new cases nationwide in the U.S., nearly doubling in prevalence over the past week, according to the data published Friday by the Centers for Disease Control and Prevention. The subvariant more than doubled as a share of cases every week through Dec. 24. In the past week, it nearly doubled from 21.7% prevalence.

Scientists and public health officials have been closely monitoring the XBB subvariant family for months because the strains have many mutations that could render the Covid-19 vaccines, including the omicron boosters, less effective and cause even more breakthrough infections.

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XBB was first identified in India in August. It quickly become dominant there, as well as in Singapore. It has since evolved into a family of subvariants including XBB.1 and XBB.1.5.

Andrew Pekosz, a virologist at Johns Hopkins University, said XBB.1.5 is different from its family members because it has an additional mutation that makes it bind better to cells.

“The virus needs to bind tightly to cells to be more efficient at getting in and that could help the virus be a little bit more efficient at infecting people,” Pekosz said.

Yunlong Richard Cao, a scientist and assistant professor at Peking University, published data on Twitter Tuesday that indicated XBB.1.5 not only evades protective antibodies as effectively as the XBB.1 variant, which was highly immune evasive, but also is better at binding to cells through a key receptor.

Scientists at Columbia University, in a study published earlier this month in the journal Cell, warned that the rise of subvariants such as XBB could “further compromise the efficacy of current COVID-19 vaccines and result in a surge of breakthrough infections as well as re-infections.”

The XBB subvariants are also resistant to Evusheld, an antibody cocktail that many people with weak immune systems rely on for protection against Covid infection because they don’t mount a strong response to the vaccines.

The scientists described the resistance of the XBB subvariants to antibodies from vaccination and infection as “alarming.” The XBB subvariants were even more effective at dodging protection from the omicron boosters than the BQ subvariants, which are also highly immune evasive, the scientists found.

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