Jan. 5—A new Omicron subvariant, XBB 1.5, now makes up the vast majority of new cases in New England, rapidly outcompeting the previous BA.4 and BA.5 variants. The XBB 1.5 variant was first detected in the region in mid-November.

Just seven weeks later, XBB 1.5 makes up approximately 80% of new cases according to the Centers for Disease Control and Prevention variant tracker. This coincided with an 89% increase in COVID-19 hospitalizations since Thanksgiving.

"The only change in our hospital is that there's more [COVID]," said Dr. Ulysses Wu, Hartford HealthCare chief epidemiologist. "That would be consistent because this variant can affect people easier, but we have to take that into context because we're in the middle of winter."

Seasonal surges

While seasonal, post-holiday surges are expected this time of year, the new variant is still cause for concern. Research published in the journal Cell indicates that XBB is "pan resistant" to neutralizing antibodies which prevent infection.

"Our data demonstrate that these new subvariants were barely susceptible to neutralization by sera from vaccinated individuals with or without prior infection, including persons recently boosted with the new bivalent mRNA vaccines," the study authors write. "XBB sublineages have evolved additional mutations that are seemingly, "filling the holes" that allow a few monoclonal antibodies to get through and neutralize their Omicron predecessors."

The study authors warn that this immune evasion could lead to a "surge in breakthrough infections as well as re-infections." Repeat COVID-19 infection is associated with increased risk of severe symptoms and long COVID.

Boosters

Preliminary data also suggests that XBB 1.5 can bind to human cells better than its predecessor strains. According to Akiko Iwasaki, director of the Center for Infection & Immunity at the Yale School of Medicine this could potentially give the virus ability to cause infection in more types of cells in more tissue types across the body.

While alarming, that isn't the final word on this new variant. Another study, published in the New England Journal of Medicine found that while neutralizing antibodies from vaccinated and boosted patients were less effective against XBB, the bivalent booster was still able to neutralize XBB 1.5.

"It's a good sign that the bivalent boosters seem to work," said study author Mehul Suthar, a professor of pediatrics at the Emory School of Medicine. "But there's always going to be a concern when you try to fix one problem in BA.5 but then you have a new variant that ... can simply just evade antibody responses better."

Suthar recommended the best option for protection is a bivalent booster. Old boosters, and the original versions of the COVID-19 vaccine are probably not sufficient to prevent severe illness.

"We have to use the tools we have at hand," said Suthar. "I think getting the bivalent booster is going to improve the ability of your immune system to combat XBB 1.5 ... Employing other strategies like masking and social distancing in high-risk situations is certainly advisable."

Since this new variant is antibody evasive, monoclonal antibodies won't work. New monoclonal antibodies would need to be isolated and developed.

Still, early research from the University of Minnesota found that antiviral drugs, like Paxlovid, were still effective for treating the new variants. Even with reduced efficacy, the bivalent booster still helps. And masks can further reduce both catching and spreading the virus.

Immunity

The final thing to keep in mind about new variants is that all the early research is going to focus on neutralizing antibodies. UConn virology and vaccinology professor Paulo Verardi explained that neutralizing antibodies are the lowest hanging fruit. They're by far the easiest thing for scientists to study.

"We're always looking at neutralizing antibodies, but you have to remember cell-mediated immunity," said Verardi. He explained that all the other things the immune system does to clear an infection, or develop immune memory, are much harder to nail down. "When it comes to that we may be better off than we think."

This cellular immunity and immune memory might be the reason why we haven't yet seen a surge on par with the original omicron surge last year. Most people have already been infected or vaccinated or both which might curb severe infections overall.

"I don't expect hospitalizations to rise, even with this new variant, to the level it was in previous years," said Dr. Wu. "People should not go crazy over the variant... They should still continue to do the things they should be doing to not get COVID."

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