The XBB.1.5 omicron subvariant, currently dominant in the U.S., is the most contagious version of Covid-19 to date, though it does not seem to cause more severe illness, according to the World Health Organization (WHO).
Maria Van Kerkhove, the WHO’s Covid-19 technical lead, expressed concern about the rapid spread of the subvariant in the northeastern U.S.
The number of infections with XBB.1.5 has been doubling approximately every two weeks, making it the predominant variant in the country.
“It is the most transmissible subvariant that has been detected yet,” Van Kerkhove stated during a press conference in Geneva on Wednesday. “The reason for this is the mutations within this subvariant of omicron, which allow the virus to adhere to cells and replicate easily.”
XBB.1.5 has been identified in 29 countries so far, but it could be even more widespread due to the decline in genomic sequencing globally, making tracking more challenging, Van Kerkhove noted.
While the WHO currently lacks data on the severity of XBB.1.5, there is no indication that it causes more severe illness than previous omicron versions.
The WHO’s advisory group that monitors Covid variants is conducting a risk assessment of XBB.1.5, which will be published soon, Van Kerkhove said.
“The more this virus circulates, the more opportunities it will have to change,” Van Kerkhove emphasized.
“We do expect further waves of infection around the world, but that doesn’t have to translate into further waves of death because our countermeasures continue to work.”
Scientists report that XBB.1.5 is as adept at evading antibodies from vaccines and previous infections as its relatives XBB and XBB.1, two of the most immune-evasive subvariants yet.
However, XBB.1.5 has a mutation that enhances its ability to bind tightly to cells, giving it a growth advantage.
While XBB.1.5 spreads rapidly in the U.S., China is experiencing a surge in cases and hospitalizations following the abandonment of its zero-Covid policy in response to social unrest late last year.
U.S. and global health officials have criticized Beijing for not sharing enough data about the surge with the international community.
“We continue to ask China for more rapid, regular, reliable data on hospitalizations and deaths as well as more comprehensive real-time viral sequencing,” WHO Director-General Tedros Adhanom Ghebreyesus said during the Geneva briefing.
A growing number of countries, including the U.S., now require airline passengers from China to test negative for Covid before boarding their flights.
China’s foreign ministry has argued that these measures lack scientific basis and has accused governments of politicizing Covid. However, the WHO director-general said such requirements are understandable given the limited data from China.
“With circulation in China so high and comprehensive data not forthcoming, it’s understandable that some countries are taking steps they believe will protect their own citizens,” Tedros remarked on Wednesday.
Beijing’s Center for Disease Control and Prevention shared data with the WHO on Tuesday indicating that BA.5 sublineages, specifically BA.5.2 and BF.7, account for about 98% of all infections in China.
However, Van Kerkhove pointed out that China is not sharing enough sequencing data from across its vast territory.
“It’s not just a matter of knowing what variants are circulating,” Van Kerkhove said. “We need the global community to assess these, to look at mutation by mutation to determine if any of these are new variants circulating in China but also around the world.”
