The XBB.1.5 omicron subvariant currently dominating the US is the most contagious version of Covid-19 to date, but it doesn’t appear to be making people sicker, according to the World Health Organization.
Maria Van Kerkhove, the WHO’s Covid-19 technical lead, said global health officials are concerned about how quickly the subvariant is spreading in the northeastern US. The number of people infected with XBB.1.5 doubles in the US approximately every two weeks, making it the most common variant circulating in the country.
“It is the most transmissible subvariant detected so far,” Van Kerkhove told reporters at a press conference in Geneva on Wednesday. “The reason for this is the mutations that are within this subvariant of omicron that allow this virus to attach to the cell and replicate easily.”
It has been detected in 29 countries so far, but it could be even more widespread, Van Kerkhove said. Tracking Covid variants has become difficult as genomic sequencing is declining around the world, she said.
The WHO does not yet have data on the severity of XBB.1.5, but there is currently no evidence that it makes people more sick than previous versions of omicron, Van Kerkhove said. The WHO advisory group monitoring Covid variants is conducting a risk assessment on XBB.1.5 which it will publish in the coming days, she said.
“The more this virus circulates, the more chances it will have to change,” Van Kerkhove said. “We expect even more waves of infection around the world, but that may not translate into new waves of deaths, as our countermeasures continue to work.”
Scientists say XBB.1.5 is about as good at evading vaccine and infection antibodies as its relatives XBB and XBB.1, which were two of the most immune-evading subvariants yet. But XBB.1.5 has a mutation that makes it more tightly bound to cells, giving it a growth advantage.
As XBB.1.5 spreads rapidly in the US, China is experiencing a surge in cases and hospitalizations after abandoning its zero-Covid policy late last year in response to social unrest. US and global health officials have said Beijing is not sharing enough data on the rise with the international community.
“We continue to ask China for faster, regular reliable data on hospitalizations and deaths, as well as more comprehensive real-time viral sequencing,” WHO director-general Tedros Adhanom Ghebreyesus told reporters in Geneva on Wednesday.
A growing number of countries, including the US, are requiring airline passengers from China to test negative for Covid before boarding their flights. China’s foreign ministry has said such measures have no scientific basis and has accused governments of manipulating Covid for political purposes. But the WHO director-general said the requirements are understandable given the limited data coming out of China.
“With circulation in China so large and comprehensive data lacking, it is understandable that some countries are taking steps that they believe will protect their own citizens,” Tedros said on Wednesday.
Beijing’s Center for Disease Control and Prevention shared data with WHO on Tuesday showing that BA.5 sublines, BA.5.2 and BF.7, account for about 98% of all infections in the country. But Van Kerkhove said China is not sharing enough sequencing data from the vast country.
“It’s not just about knowing which variants are in circulation,” says Van Kerkhove. “We need the global community to assess these, to look at mutation by mutation to determine whether any of these new variants are circulating in China, as well as around the world.”