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The scientists say the Covid Omicron XBB.1.5 variant is rapidly becoming dominant in the US because it is highly immune evasive and appears to be more effective at binding to cells than related sub-variants.
XBB.1.5 now accounts for about 41% of new cases nationwide in the U.S., with prevalence nearly doubling in the past week, according to data released Friday by the Centers for Disease Control and Prevention. The subversion more than doubled as a proportion of cases each week through December 24. In the last week, it has almost doubled from 21.7% prevalence.
Scientists and public health officials have been closely monitoring the XBB subspecies family for months because the strains have a number of mutations that could make Covid-19 vaccines, including omicron boosters, less effective and lead to more breakthrough infections.
XBB was first identified in India in August. It quickly became dominant there, as well as in Singapore. It has since evolved into a family of sub-variants including XBB.1 and XBB.1.5.
Andrew Pekosz, a virologist at Johns Hopkins University, said XBB.1.5 differs from its family members because it has an additional mutation that makes it better at binding to cells.
“The virus needs to bind tightly to cells to be more efficient at getting in, and that could help make the virus a little more efficient at infecting humans,” Pekosz said.
Yunlong Richard Cao, a scientist and assistant professor at Peking University, posted data on Twitter on Tuesday showing that XBB.1.5 not only evaded protective antibodies as effectively as the highly immune-evading version of XBB.1, but also better at binding to cells through a key receptor.
Scientists at Columbia University, in a study published earlier this month in the journal Cellwarned that the rise of subvariants such as XBB “could further compromise the effectiveness of current vaccines against COVID-19 and lead to an increase in breakthrough infections and reinfections.”
The XBB sub-variants are also resistant to Evusheld, the antibody cocktail that many people with weak immune systems rely on to protect against Covid because they don’t react strongly to vaccines.
The scientists described the resistance of the XBB subvariants to antibodies from vaccination and infection as “alarming”. The scientists found that the XBB sub-variants were even more effective at evading protection against omicron promoters than the BQ sub-variants, which are also highly immune.
dr. David Ho, author of the Columbia study, agreed with other scientists that XBB.1.5 likely has a growth advantage because it binds to cells better than its XBB counterparts. Ho also said that XBB.1.5 is about as immune-evasive as XBB and XBB.1, which have so far been the two subvariants most resistant to protective antibodies against infection and vaccination.
dr. Anthony Fauci, who is leaving his role as the White House’s chief medical adviser, has already said that the XBB subversions “reduce the protection that the boosters provide against infection many times over.”
“You could expect some protection, but not optimal protection,” Fauci told reporters during a White House briefing in November.
Fauci said he was encouraged by the case of Singapore, where there was a large increase in XBB infections, but the number of hospitalizations did not rise at the same rate. Pekosz said XBB.1.5 combined with holiday travel could cause a spike in U.S. cases, but said the boosters appear to prevent severe illness.
“It really looks like a vaccine, the bivalent booster provides ongoing protection against hospitalization with these variants,” Pekosz said. “It really highlights the need to get a booster, especially in vulnerable populations, to ensure continued protection against severe disease with these new variants.”
Health officials in the US have repeatedly urged the elderly in particular to take care of theirs are up to date on their vaccines and are being treated with the antiviral drug Paxlovid if they have a breakthrough infection.
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