Omicron XBB.1.5 is essentially the most transferrable sub-variant in accordance with WHO

Trunk XBB.1.5, January 4, 2023, Suqian, Jiangsu, China.

CFOTO | Future Publishing | Getty Images

The XBB.1.5 omicron subvariant currently dominating the US is the most contagious version of Covid-19 yet, but according to the World Health Organization it doesn’t appear to be making people sicker.

Maria Van Kerkhove, the WHO’s technical lead for Covid-19, said global health officials are concerned about how quickly the subvariant is spreading in the US northeast. The number of people infected with XBB.1.5 in the US has been doubling about every two weeks – it is the most widespread variant in the country.

“It is the most transmissible subvariant discovered so far,” said Van Kerkhove during a press conference in Geneva on Wednesday. “The reason for this is the mutations in this subvariant of Omicron, which allow this virus to stick to the cell and replicate easily.”

It has been detected in 29 countries so far, but it could be more widespread, Van Kerkhove said. Tracking Covid variants has become difficult as genome sequencing declines around the world, she said.

The WHO doesn’t have data on the severity of XBB.1.5 yet, but there’s no evidence at the moment that it makes people sicker than previous versions of omicron, Van Kerkhove said. The WHO advisory group tracking 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 opportunities it will have to change,” said Van Kerkhove. “We expect further waves of infections around the world, but this need not lead to further waves of deaths because our countermeasures continue to work.”

Scientists say XBB.1.5 is about as good at dodging antibodies from vaccines and infections as its relatives XBB and XBB.1, which were two of the most immune-avoidable subvariants to date. But XBB.1.5 has a mutation that makes it bind more tightly to cells, giving it a growth advantage.

While XBB.1.5 is spreading rapidly in the US, China is grappling with a surge in cases and hospitalizations after abandoning its zero-Covid policy in response to social unrest late last year. US and global health officials said Beijing is not sharing enough data on the surge with the international community.

“We continue to ask China for faster, regular and reliable data on hospitalizations and deaths, as well as more comprehensive real-time virus sequencing,” WHO Director-General Tedros Adhanom Ghebreyesus told reporters in Geneva on Wednesday.

More and more countries, including the US, are requiring passengers from China to test negative for Covid before boarding their flights. China’s Foreign Ministry said such measures lacked any scientific basis and governments have been accused of manipulating Covid for political ends. But the WHO director-general said the requirements are understandable given the limited data from China.

“Given the level of prevalence in China and the lack of comprehensive data, it is understandable that some countries are taking steps that they believe will protect their own citizens,” Tedros said on Wednesday.

The Beijing Center for Disease Control and Prevention on Tuesday shared data with the WHO showing that the BA.5 sublineages, BA.5.2 and BF.7, account for about 98% of all infections in the country. However, Van Kerkhove said China is not sharing enough sequencing data from across the vast country.

“It’s not just about knowing which variants are in circulation,” said Van Kerkhove. “We need the global community to evaluate these, to study mutation by mutation to determine if any of these new variants are new variants that are circulating in China but also around the world.”

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