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The researchers say the Covid omicron XBB.1.5 variant is rapidly becoming dominant in the US because it is extremely resistant to evasion and appears to be more efficient at binding to cells than related sub-variants.
According to data released Friday by the Centers for Disease Control and Prevention, XBB.1.5 now accounts for about 41% of recent cases nationwide in the US, nearly doubling the incidence over the past week. The subvariant greater than doubled as a share of cases every week through December 24. Last week it nearly doubled with 21.7% adoption.
Scientists and public health officials have been closely monitoring the XBB subvariant family for months, as these strains have multiple mutations that would make Covid-19 vaccines, including those who resemble omicrons, less effective and cause much more breakthrough infections.
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XBB was first identified in India in August. It quickly became dominant there, as in Singapore. It has since evolved right into a family of sub-variants including XBB.1 and XBB.1.5.
Andrew Pekosz, a virologist at Johns Hopkins University, said that XBB.1.5 differs from members of its family because it has a further mutation that makes it bind better to cells.
“The virus needs to bind tightly to the cells to get in additional efficiently, and this will help the virus to be a bit more practical at infecting people,” said Pekosz.
Yunlong Richard Cao, a researcher and assistant professor at Peking University, tweeted data on Tuesday that indicates that XBB.1.5 not only evades protective antibodies as effectively because the XBB.1 variant, which was highly resistant to evasion, but in addition binds better to from the cell via a key receptor.
Researchers at Columbia University, in a study published earlier this month within the journal Cell, warned that the rise of subvariants akin to XBB could “further weaken the effectiveness of current COVID-19 vaccines and cause a spike in breakthrough infections in addition to re-infections.” “
The XBB subvariants are also resistant to Evusheld, a cocktail of antibodies that many individuals with weak immune systems depend on for defense against Covid infection because they don’t elicit a robust response to vaccines.
The researchers described the resistance of the XBB subvariants to antibodies from vaccination and infection as “worrying”. The researchers found that the XBB subvariants were even more practical at evading protection from omicron enhancers than the BQ subvariants, that are also highly resistant to evasion.
Dr. David Ho, writer 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 relatives. Ho also said that XBB.1.5 is about as immune evasive as XBB and XBB.1, which have been the 2 most resistant subvariants to protective antibodies against infection and vaccination to this point.
Dr. Anthony Fauci, who’s stepping down because the White House’s chief medical adviser, previously said that XBB subvariants reduce “manyfold” the protection provided by boosters against infection.
“Some protection will be expected, but not optimal,” Fauci told reporters during a White House briefing in November.
Fauci said he was encouraged by the case of Singapore, which saw a major increase in infections from XBB, but didn’t see hospitalizations increase at the identical pace. Pekosz said that XBB.1.5 combined with holiday travel could cause a rise in cases within the US.
“It seems that the vaccine, bivalent booster, provides ongoing protection against hospitalization with these variants,” said Pekosz. “This really underscores the necessity for reinforcing particularly vulnerable populations to ensure continued protection against severe disease with these latest variants.”
US health officials have repeatedly urged, especially the elderly, to make sure that they stay awake to date on their vaccines and receive Paxlovid antiviral treatment in the event that they have a breakthrough infection.