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new covid subvariant xbb.1.5 is 'most transmissible' yet

singapore was hit hard by the new variant, which is very contagious, but the number of hospitalizations didn't rise.

by maija kappler

published jan 06, 2023

3 minute read

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3 minute read

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what you need to know about xbb.1.5, the new omicron subvariant

canada's high vaccination rate is promising for public health. getty

xbb.1.5, a new omicorn subvariant, is the “most transmissible subvariant that has been detected yet,” according to the world health organization (who). maria van kerkhove, an epidemiologist and the who’s technical lead on covid, told reporters at a press conference in geneva on wednesday that the subvariant is spreading at an alarming rate.

“we are concerned about its growth advantage,” van kerkhove said. xbb.1.5 was first detected in the u.s., where it has spread considerably, and has since been identified in 29 other countries.

“we do expect further waves of infection around the world, but that doesn’t have to translate into further waves of death because our countermeasures continue to work,” she added.

xbb.1.5 likely emerged when someone was infected with two different kinds of omicron at the same time, dr. ewan harrison of the wellcome sanger institute in cambridge told bbc news: “a bit of the genome from one virus gets joined up with another bit from a second virus, and they merge, and that goes on to transmit.”

how does xbb.1.5 work?

xbb.1.5 grips very tightly to our cells, which lets it avoid our antibodies, science writer katherine j. wu explains in the atlantic. that allows the virus to replicate easily. but the good news is that the mutation, called f486p, also reduces the virus’ ability to infect our cells, bbc news says.

and while the subvariant is easier to catch than previous strains, there are currently no signs that it causes more severe illness than any other strain. singapore was hit hard by the very similar xbb strain in the fall, but hospitalizations didn’t rise significantly in the country.

“i think there’s less to be worried about” with xbb.1.5 than with the first omicron wave just over a year ago, emory university immunologist mehul suthar told the atlantic. “my previous exposures are probably going to help against any xbb infection i have.”

the atlantic also reported that in the last week of december, xbb.1.5 grew from making up an estimated 20 per cent of u.s. covid cases to 40 per cent. “that’s the big thing everybody looks for — how quickly it takes over from existing variants,” shaun truelove, an infectious-disease modeler at johns hopkins university, told the magazine. “and that’s a really quick rise.”

while the subvariant has been detected in canada, it’s not yet clear how widespread it’s become. earlier this week, the public health agency of canada told cbc news that “at this time, it is too early to tell” whether it’s replicating as fast on this side of the border. but the who says it’s likely to spread globally.

even if it does become the primary strain in canada, this country’s high vaccination rate — 83 per cent of the country has had at least one dose, and 80 per cent have had the primary vaccine series (two doses) — is promising for public health. david heymann of the london school of hygiene and tropical medicine told bbc news that areas with high vaccination levels as well as previous covid infections aren’t likely to suffer severe problems with xbb.1.5. it’s places like china, where vaccination rates are low and there’s less natural immunity, that are more likely to see big problems, he said.

that’s a major reason global vaccine equity is important: containment is crucial for everyone, van kerkhove said.

“the more this virus circulates, the more opportunities it will have to change.”

maija kappler is a reporter and editor at healthing.

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new covid subvariant xbb.1.5 is 'most transmissible' yet

singapore was hit hard by the new variant, which is very contagious, but the number of hospitalizations didn't rise.

how does xbb.1.5 work?

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new covid subvariant xbb.1.5 is 'most transmissible' yet

singapore was hit hard by the new variant, which is very contagious, but the number of hospitalizations didn't rise.

how does xbb.1.5 work?

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