Epidemiologist breaks down newest COVID-19 variant, the most contagious to date

The newest strain of the novel coronavirus may be the most transmissible yet.

The latest variant, named XBB.1.5, is an offshoot of the BA.1 variant of Omicron. Since the first case was reported in New York City around Thanksgiving, XBB.1.5 has spread rapidly, increasing from 2% of U.S. COVID-19 cases in December to 27% in early January.

Susan Hassig, an epidemiologist at Tulane University School of Public Health and Tropical Medicine, said the virus’ high transmissibility means it will “push out the other Omicron strains fairly soon” and that the cessation of community testing has made tracking XBB.1.5 more difficult.

“We really have a limited view into the actual burden of infection with the virus generally, and new variants in particular,” Hassig said. “Currently approximately 3% of all ER visits are testing positive for coronavirus infection. Wastewater testing for coronavirus at the community level shows 50-55% of testing sites seeing increasing virus levels but this testing is not done uniformly or universally.”

It’s hard to predict what will happen next as XBB.1.5 spreads, Hassig said. While the virus has been most prevalent in the Northeastern U.S., Hassig has not seen excessively high rates of severe illness yet.

“Lots of people will miss work or school and hospitalizations and deaths will likely be elevated, but there’s no way to know how high,” Hassig said. “And then what will happen with long COVID/post-COVID conditions is totally unknowable.”

The XBB.1.5 is completely resistant to bebtelovimab, Evusheld and other monoclonal antibody treatments. According to an article published in Cell, XBB.1.5 evades antibodies due to 14 new mutations to the spike protein, which also allow the virus to better bind to cells.

While Paxlovid, an antiviral therapeutic, is effective against the new strain, Hassig said the best way to stay safe is to get boosted with a bivalent COVID-19 vaccine and immediately get tested if you show signs of a respiratory illness.

“Bivalent vaccinated people continue to die at lower rates than vaccinated but un-boosted, and both of those groups at much lower rates than the unvaccinated,” Hassig said. “We are now seeing 300-400 deaths a day from COVID, the equivalent of 1-2 planes crashing each day. Many would be avoidable with wider uptake of vaccine and early diagnosis and treatment.”

Hassig is available for media interviews on the XBB.1.5 variant of COVID-19 and related issues. She can be reached at shassig@tulane.edu.