Health Experts Warily Eye XBB.1.5, the Latest Omicron Subvariant - The New York Times - 0 views
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Most recombinant SARS-CoV-2 viruses have dwindled away in a matter of weeks or months, unable to outcompete other lineages. XBB, on the other hand, got a winning ticket in the genetic lottery.
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From one parent, it gained a set of mutations that helped it evade antibodies from previous infections and vaccinations. From the other parent, it gained a separate set of mutations that made it even more evasive.
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“XBB literally picked up the most possible mutations that it could possibly pick up from those two parents,” said Thomas Peacock, a virologist at Imperial College London. The new combination made XBB one of the most evasive Omicron subvariants in existence last summer.
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Recent experiments suggest that XBB paid a steep price for its power to evade immunity. The mutations allow it to escape antibodies by altering the shape of the protein, called spike, that covers its surface. But some of those mutations also make it harder for XBB spike proteins to grab tightly to cells — the first step required for an infection.
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That loose grip may have lessened XBB’s advantage against other forms of the virus. In late 2022, it jostled alongside a number of other Omicron subvariants. In Singapore, XBB caused a surge in October, for example, while remaining rare in many other parts of the world.
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As XBB multiplied, it continued to mutate into new forms. The earliest samples of XBB.1.5 were isolated in October in New York. The new subvariant gained one crucial mutation, known as F486P.
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Yunlong Cao of Peking University and his colleagues tested out XBB.1.5 in dishes of cells, comparing how it fared against earlier forms of XBB. The researchers found that the F486P mutation allowed XBB.1.5 to grab tightly to cells again. But the new subvariant could still evade antibodies as well as earlier forms of XBB.
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In Connecticut, for example, Nathan Grubaugh at Yale University and his colleagues found that by mid-December, other Omicron subvariants were falling. Only XBB.1.5 cases were growing. Dr. Grubaugh estimates that it is about 20 percent more transmissible than BQ.1, which had been the dominant form.
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How severe XBB.1.5 infections are compared with other forms of the coronavirus is not yet clear. “It’s serious,” Dr. Grubaugh said. “I just don’t necessarily know if it’s really more serious than some of the other Omicron lineages in terms of the overall impact.”
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XBB.1.5 has already spread to other countries, and is growing rapidly in Germany, Denmark and elsewhere in Europe
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Scientists are already scanning new sequences being uploaded to an international database called GISAID in the hopes of spotting an upgraded version of XBB.1.5. But their job is getting harder because governments are pulling back on sequencing efforts. “Worldwide, sequencing has taken a real hit,” Dr. Peacock said.
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The United States, which once lagged behind other nations, has managed to maintain a fairly strong sequencing effort. Without it, Dr. Peacock said, XBB.1.5 might have stayed below the radar for much longer. If XBB.1.5’s next generation is evolving somewhere with little sequencing, it may go undetected for some time to come.
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Dr. Lemieux said that paring back on sequencing was a mistake, given how many infections and deaths the virus is still causing. “This is a part of public health,” he said.