(NEXSTAR) – For nearly a month, the U.S. has been dealing with a new, now-dominant COVID variant, XBB.1.5. The latest data from the Centers for Disease Control and Prevention shows that, while it had previously been prevalent in one region of the U.S., it’s beginning to spread in others.

XBB.1.5 is a spinoff of XBB, a subvariant of omicron that health officials worldwide have been warning about since the fall. XBB.1.5 is considered a recombinant virus because it carries genetic data from two previous mutations, Nexstar’s The Hill reports.

XBB was first detected in India in August and spread quickly through Southeast Asia, according to the World Health Organization. At the time, the WHO described XBB as “the most antibody-evasive SARS-CoV-2 variant identified to date.”

Since first being discovered, XBB has evolved and now has two subvariants, XBB.1 and XBB.1.5. XBB.1.5 differs from its family members because it has a mutation that allows it to better bind to cells, Andrew Pekosz, a virologist for Johns Hopkins University, told CNBC. That ability to bind gives it a better chance of infecting people.

Earlier this month, XBB.1.5 began sweeping through the Northeast. As of Thursday, the CDC reports the variant makes up roughly 82% of cases in New England, New York, and New Jersey. It’s now becoming more prevalent across states along the East Coast.

According to the CDC, XBB.1.5 makes up roughly half of the cases being reported through Delaware, the District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia. Further south – across the Carolinas, Tennessee, Kentucky, Alabama, Florida, Georgia, and Mississippi – XBB.1.5 comprises roughly one-third of cases. It isn’t dominant in this region – BQ.1.1 is at roughly 38% of cases, but CDC data shows its prevalence is declining.

BQ.1.1, a substrain of omicron as well, is the most common variant across the rest of the country so far. As it is in the south, the variant has been declining in prevalence nationally as XBB.1.5 has spread. As more data is collected from states, this data could change, the CDC notes.

So far, XBB.1.5 hasn’t proven to be more severe than others, Dr. Barbara Mahon, director of the CDC’s proposed Coronavirus and Other Respiratory Viruses Division said during an interview with CBS News. The World Health Organization echoed those sentiments last week.

Studies have suggested, though, that it may not respond as well to antibody treatment as other variants and subvariants have. According to Dr. Jay Varma of the Cornell Center for Pandemic Prevention and Response, the monoclonal antibodies treatment “is no longer effective,” leaving healthcare providers with Paxlovid, “the one drug that’s widely available, as our effective treatment option.”

Mahon said the bivalent booster is expected to be as effective at protecting against XBB.1.5 as it has with other omicron subvariants.

Late last month, the FDA warned an at-home saliva testing kit, DxTerity, has been found to “have significantly reduced sensitivity” to some omicron mutations, including the XBB, BA.2.75, and BN.1.

Medical professionals and the CDC continue to recommend wearing a mask, getting vaccinated, and staying home if you aren’t feeling well — even if you’re testing negative for COVID.