A new offshoot strain, XBB.1.5, of the COVID-19 Omicron variant has been found to have “alarming” immunity evasion, which could cause another surge of cases in the United States, according to experts.

Dr. David Ho, professor of microbiology and immunology at Columbia University, said the XBB.1 offshoot variant is 63 times less likely to be neutralized by the antibodies in people who have either been infected by COVID-19 or have been vaccinated against the virus when compared to the BA.2 variant. The same is the case with the XBB.1.5 strain.

“It is alarming that these newly emerged subvariants could further compromise the efficacy of current COVID-19 vaccines and result in a surge of breakthrough infections as well as re-infections,” Dr. Ho wrote in his findings, which were recently published in the journal Cell.

In addition to its high immune evasion, the XBB.1.5. also has a key mutation at site 486, allowing it to bind better to ACE2, which is the door the virus uses to enter human cells. This mutation means the offshoot variant is more infectious.

“The mutation is clearly letting XBB.1.5 spread better,” Jesse Bloom, a computational virologist at the Fred Hutchinson Cancer Center, wrote in an email to CNN.

Experts are now warning that the strain’s features could give it the ability to cause another surge of COVID-19 cases in the U.S.

As of Friday last week, the U.S. Disease Control and Prevention (CDC) estimated that the XBB.1.5 variant accounted for 41% of new COVID-19 infections throughout December.

In northeastern states, the CDC said the offshoot variant is causing about 75.3% of all new cases. Those states include Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont.

In New York and New Jersey, the XBB.1.5 strain caused 72.2% of cases during the last week of December.

As of Tuesday, the U.S. reported a total of 100,845,043 COVID-19 cases since the pandemic began in 2020. Among those, 1,093,971 have died of the virus, according to data from Johns Hopkins University.