The fast-spreading omicron subvariant XBB.1.5 is estimated to account for 43% of the COVID-19 cases in the United States for the week ended Jan. 14, data from the Centers for Disease Control and Prevention showed on Friday.

The subvariant accounted for about 30% of cases in the first week of January, higher than the 27.6% the CDC estimated last week.

XBB.1.5, which is related to omicron, is currently the most transmissible variant. It is an offshoot of XBB, first detected in October, which is itself made from a combination of two other omicron subvariants.

The World Health Organization (WHO) said earlier this week XBB.1.5 may spur more COVID-19 cases based on genetic characteristics and early growth rate estimates.

While it is unclear if XBB.1.5 can cause its own wave of global infections, experts say the current booster shots continue to protect against severe symptoms, hospitalization and death.

WHO Director General Tedros Adhanom Ghebreyesus tweeted last week the subvariant has been on the rise globally and has been identified in over 25 countries.

The rise in the new variant correlated with an uptick in COVID-19 cases in United States over the last six weeks.

Increased prevalence of XBB.1.5 cases has eclipsed the previously dominant omicron subvariant BQ.1.1 and BQ.1, which were offshoots of BA.5. The two strains together accounted for 44.7% of cases in the United States in the week ended Jan. 14, compared with 53.2% a week ago, the CDC said.