Omicron XBB.1.5 has no mutations known to make humans sicker

A man receives a Covid-19 test at a mobile Covid-19 testing site as people queue in Times Square in New York City on December 6, 2021.

Tayfun Coskun | Anadolu Agency | Getty Images

The subvariant omicron XBB.1.5 has no mutations known to make people sicker when they contract the virus, according to a World Health Organization risk assessment released on Wednesday.

However, the WHO noted in the report that it has no real data on how XBB.1.5 affects patient health, so it cannot currently draw any conclusions about the severity of the subvariant.

The WHO said XBB.1.5 is one of the Covid subvariants most adept at dodging immunity from vaccination or infection. It is just as immune evasive as another subvariant of its family, XBB.1., which was the Covid variant best at dodging antibodies that block infection.

The global health organization said XBB.1.5 has a growth advantage in the US, particularly in the Northeast where it has quickly become dominant. XBB.1.5 could cause cases to increase globally, but it’s difficult to know for sure as almost all the data comes from the US, according to the WHO. The organization said it needs more data on how fast XBB.1.5 is spreading to other countries.

Maria van Kerkhove, the WHO’s technical lead for Covid-19, said last week that XBB.1.5 was the best transmissible Covid subvariant to date. Scientists believe it has a growth advantage because it’s highly immune-avoidable and binds more tightly to human cells, making it more contagious.

“It’s the most transmissible subvariant discovered so far,” Van Kerkhove told reporters during a news conference in Geneva last 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.”

In the US, XBB.1.5 is the only sub-variant currently showing significant growth. It rose from about 2% of cases in early December to almost 28% in the first week of January, according to data from the Centers for Disease Control and Prevention. It causes more than 70% of new Covid cases in the North East.

Data on how well the XBB.1.5 vaccines hold up is currently limited, although the subvariant is expected to cause more breakthrough infections. Laboratory studies have shown that other variants in the XBB family have proven adept at evading the antibodies generated by vaccination with the Omicron boosters.

Although subvariants of omicron have been shown to cause breakthrough infections, Pfizer’s and Moderna’s vaccines still generally prevent hospitalizations and deaths. However, public health officials in the US have emphasized that staying up to date on their vaccinations is especially important for vulnerable groups such as the elderly to avoid serious illnesses.

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