According to Maria Van Kerkhove, WHO's Covid-19 technical lead, global health officials are concerned about how quickly the subvariant is spreading in the northeastern United States. In the United States, the number of people infected with XBB.1.5 has been doubling every two weeks, making it the most common variant circulating in the country.
"It is the most transmissible subvariant discovered to date," Van Kerkhove said at a press conference in Geneva on Wednesday. "The reason for this is that the mutations within this subvariant of omicron allow this virus to easily adhere to the cell and replicate."
It has been detected in 29 countries so far, but Van Kerkhove believes it could be much more widespread. She claims that tracking Covid variants has become more difficult as global genomic sequencing has declined.
The WHO does not yet have data on the severity of XBB.1.5, but there is no indication that it makes people sicker than previous versions of omicron, according to Van Kerkhove. The WHO's Covid advisory group is conducting a risk assessment on XBB.1.5, which will be published in the coming days, she said.
"The more this virus spreads, the more chances it has to change," Van Kerkhove said. "We expect more waves of infection around the world, but this does not have to translate into more waves of death because our countermeasures are still effective."
According to scientists, XBB.1.5 is about as good at evading antibodies from vaccines and infection as its XBB and XBB.1 relatives, which were two of the most immune evasive subvariants discovered so far. However, XBB.1.5 has a mutation that causes it to bind more tightly to cells, giving it a growth advantage.
As XBB.1.5 spreads rapidly in the United States, China is dealing with an increase in cases and hospitalizations after abandoning its zero-Covid policy in response to social unrest late last year. According to US and global health officials, Beijing is not sharing enough data on the outbreak with the international community.
"We continue to request from China more rapid, consistent, and reliable data on hospitalizations and deaths, as well as more comprehensive real-time viral sequencing,"
A growing number of countries, including the United States, are requiring Chinese airline passengers to be Covid-free before boarding their flights. China's foreign ministry has stated that such measures lack scientific foundations and that governments are manipulating Covid for political purposes. However, given the limited data coming out of China, the WHO director-general stated that the requirements are understandable.
The Center for Disease Control and Prevention in Beijing shared data with the WHO on Tuesday, indicating that BA.5 sublineages, BA.5.2 and BF.7, account for approximately 98% of all infections in the country. Van Kerkhove, on the other hand, claims that China is not sharing enough sequencing data from across the vast country.
"It's not just a matter of knowing which variants are out there," Van Kerkhove explained. "We need the global community to assess these, to look at mutation by mutation to see if any of these are new variants circulating in China and elsewhere."