New York City health officials are warning residents that the infectious omicron subvariant XBB.1.5 may be more likely to infect people who have already been vaccinated or infected with COVID-19.
"Omicron subvariant XBB.1.5 now accounts for 73% of all sequenced COVID-19 cases in NYC," the NYC Department of Health and Mental Hygiene tweeted on Friday. "XBB.1.5 is the most transmissible form of COVID-19 that we know of to date and may be more likely to infect people who have been vaccinated or already had COVID-19."
The department added that getting vaccinated against the virus, including receiving an updated booster shot, remains the best way to protect against hospitalization and death, including from new variants.
According to data from the Centers for Disease Control and Prevention, XBB.1.5 accounts for 43% of cases in the U.S.
COVID XBB.1.5 VARIANT NOW ACCOUNTS FOR 43% OF ALL US CASES, CDC SAYS
In the first week of January, the subvariant accounted for about 30% of cases.
XBB.1.5, an offshoot of XBB, was first detected in October.
The World Health Organization warned earlier this week that it may lead to an increased number of cases based on genetic characteristics and early growth rate estimates.
COVID OMICRON SUBVARIANT XBB: WHY THE NUMBER OF CASES IS LIKELY FAR GREATER THAN REPORTED
Scientists have cautioned that the virus will surely keep evolving.
"Our concern is how transmissible it is," Maria Van Kerkhove, the WHO's technical lead on COVID-19, said.
"The more this virus circulates, the more chances it will have to change," she noted.
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Van Kerkhove said there is no data yet to prove that XBB.1.5 causes more severe disease, but that the agency is working on a new risk assessment of the variant and expects to release it soon.
Reuters and The Associated Press contributed to this report.