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This latest variant is especially adept at dodging immune responses.

While the severity of COVID-19 has gone down in recent months thanks to increased vaccination efforts and new treatments, the CDC has not taken its eyes off the ongoing spread of the disease. Even without large-scale outbreaks, new variants are still cropping up, and one of the latest variants, has some health professionals concerned.

This new variant, codenamed XBB.1.5, is swiftly muscling out the BA and BQ variants of the virus, accounting for about 41% of new COVID cases in December. XBB has similar characteristics to the BA.2 variant that caused some minor outbreaks last spring, with a particular aptitude for dodging immune responses in all individuals vaccinated or unvaccinated. More concerning is XBB’s ability to bind to the ACE2 site of a cell, the spot where viruses typically infect healthy cells. This trick allows the virus to more-easily infiltrate our bodies and proliferate itself.

The CDC says it is tracking a new variant of concern dubbed XBB.1.5, which now makes up 40.5% of new infections across the country. https://t.co/X5LYXYw0ui

— CBS News (@CBSNews) December 30, 2022

“Most public health officials would have expected an increase in COVID-19 cases, even before we knew about XBB.1.5.” said Andrew Pekosz, a professor at Johns Hopkins Bloomberg School of Public Health who studies viral replication. “So whether the increases in COVID cases that are occurring during the holidays are occurring because of the social interactions that people have had or whether they’re specifically related to XBB.1.5 is still something that isn’t clear. Both of those things are probably contributing.”

While concerns of the efficacy of vaccines are on the table, health authorities are still urging US citizens to get the latest booster shot, as even some increased protection against the virus is better than nothing.