The first case of Omicron's highly contagious variant BQ.1 has been detected in Thailand, according to the Centre for Medical Genomics at Ramathibodi Hospital.
The centre posted on Facebook that the US Centers for Disease Control and Prevention (CDC) has issued an alert for the outbreak of BQ.1 and BQ.1.1, the two descendants of Omicron's BA.5 sub-variant.
BQ.1 now makes up one in 10 cases in the US.
Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said BQ.1 and BQ.1.1 are "pretty troublesome" and they have a concerning "doubling time", referring to how quickly they spread.
BQ.1 and BQ.1.1 are reported to be resistant to current antibody medications used to treat Covid-19 patients.
BQ.1 spreads 15% faster than BA.5.2 and 14% faster than BA.2 on a daily basis.
However, there is no proof that BQ.1 and BQ.1.1 will cause more severe infections and more fatalities than previous sub-variants, the centre said.
Previously, two cases of XBB sub-lineage were detected last month in two people: a foreign woman, 60, who arrived from Hong Kong and a Thai woman, 49, who returned from Singapore.
Each experienced mild symptoms and have already recovered.
