Illustrative image (Photo:  AFP/VNA)

Based on its genetic characteristics and early growth rate estimates, XBB.1.5 may contribute to increases in case incidence, the WHO said after a recent meeting. However, it said that it has only "low confidence" in the assessment, as the data was mostly from just one country, the United States. The WHO said China needs to share more data on its COVID-19 outbreak.

The US Centers for Disease Control and Prevention (CDC) on Tuesday warned that the sub-variant XBB.1.5 is spreading rapidly in the US. Their data indicated that XBB.1.5 was responsible for 28% of all new COVID-19 cases recorded this week, up from 18% last week.

According to researchers, XBB.1.5 is a recombinant variant of the Omicron sub-variants BA.2.10.1 and BA.2.75. XBB caused a wave of new cases in Singapore last fall.

Scientists suggest that XBB.1.5 may be able to evade any immunity generated by infection with the SARS-CoV-2 virus or a dose of COVID-19 vaccine. Although XBB.1.5 appears to be more infectious, its severity is still unknown.