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The Covid Omicron XBB.1.5 variant quickly became dominant in the US because it is highly immunogenic and appears to be more effective at binding to cells than related subvariants, scientists say.
XBB.1.5 now represents about 41% of new cases in the US, nearly doubling over the past week, according to data published Friday by the Centers for Disease Control and Prevention. The subvariant more than doubled its share of cases each week through December 24. In the last week, it almost doubled from 21.7% prevalence.
Scientists and public health officials have been monitoring the XBB subvariant family for months because the strain has mutations that can make Covid-19 vaccines, including omicron boosters, less effective and cause more 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 subvariants 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 bind to cells better.
“The virus needs to bind tightly to the cell to be more efficient in entering and that can help the virus to be more efficient in infecting people,” Pekosz said.
Yunlong Richard Cao, a scientist and assistant professor at Peking University, published data on Twitter Tuesday showing that XBB.1.5 not only evades protective antibodies as effectively as the XBB.1 variant, which is highly immune, but is also better at binding. cells through key receptors.
Scientists at Columbia University, in a study published earlier this month in the journal Cell, warned that the rise of subvariants such as XBB could “further compromise the effectiveness of the current COVID-19 vaccine and cause breakthrough infections to also increase again. – infections.”
The XBB subvariant is also resistant to Evusheld, the cocktail of antibodies that many people with weak immune systems believe protect against Covid infection because they do not respond strongly to the vaccine.
Scientists describe the resistance of XBB subvariants to antibodies from vaccinations and infections as “alarming.” The XBB subvariant is even more effective in avoiding protection from omicron boosters than the BQ subvariant, which also avoids immunity too much, the scientists found.
Dr. David Ho, author of the Columbia study, agreed with other scientists that XBB.1.5 probably has a growth advantage because it binds cells more than its XBB cousin. Ho also said XBB.1.5 is about as immune evasive as XBB and XBB.1, which are the two subvariants most resistant to protective antibodies from infection and vaccination so far.
Dr. Anthony Fauci, who left his role as the White House’s chief medical adviser, previously said that the XBB subvariant reduces the protection provided by boosters against infection “by twofold.”
“You can expect protection, but not optimal protection,” Fauci told reporters during a White House briefing in November.
Fauci said he was encouraged by the cases in Singapore, which has seen a large number of infections from XBB but has not seen hospitalizations rise at the same rate. Pekosz said XBB.1.5, in combination with holiday travel, can cause cases to rise in the US but said boosters appear to prevent severe disease.
“It looks like the vaccine, the bivalent booster provides continued protection from hospitalization with that variant,” Pekosz said. “It really emphasizes the need to get boosters especially to vulnerable populations to provide continued protection from severe disease with this new variant.”
Health officials in the US have repeatedly called on parents in particular to make sure their vaccines are up-to-date and to be treated with the antiviral Paxlovid in case of breakthrough infections.