The CDC projected Friday that about 40% of confirmed U.S. Covid cases are caused by the XBB.1.5 strain, up from 20% a week ago. In the Northeast, about 75% of confirmed cases are reported to be XBB.1.5.
It’s not clear yet where this version of omicron came from, but it appears to be spreading quickly here. There’s no indication it causes more severe illness than any other omicron virus, Dr. Barbara Mahon, director of CDC’s Coronavirus and Other Respiratory Viruses Division, told NBC News.
While overall Covid hospitalizations are rising around the country, areas such as the Northeast that have seen high levels of the new variant have not experienced a disproportionate increase in hospitalizations, Mahon said.
“We’re seeing hospitalizations have been notching up overall across the country,” she said. “They don’t appear to be notching up more in the areas that have more XBB.1.5.”
The seven-day average of daily Covid hospitalizations reached 42,140 on Friday, an increase of 4.2% from two weeks previously, according to an NBC News tally. The seven-day average of daily intensive care unit admissions has also risen to 5,125 per day, an increase of more than 9% from two weeks ago.
Daily Covid hospitalizations, 7-day average
There’s a lot that’s still unknown about the latest subvariant, including whether it’s more contagious than other forms of omicron, Mahon said.
Other scientists worry that XB.1.5 is even better at getting around the antibodies we’ve built up from Covid vaccines and previous infection from the many different types of omicron that have spread since last December, including the original BA.1 and the more recent BQ.1.1 and BQ.1 subvariants.
The XBB.1.5 is a relative of the omicron XBB variant, which is a recombinant of the omicron BA.2.10.1 and BA.2.75 subvariants.
Combined, XBB and XBB.1.5 make up 44% of cases in the U.S., crowding out other versions of omicron.
XBB has been found in at least 70 countries, according to the World Health Organization, and has caused surges of infection in some parts of Asia, including India and Singapore, in October.
Studies performed in the lab have found that XBB is capable of evading antibodies from previous Covid infections or vaccinations, meaning that being exposed to the virus would mean someone is more likely to get sick or reinfected and show symptoms.
“It’s clear that there’s immune evasive properties of XBB,” said Dr. Isaach Bogoch, an infectious disease physician and epidemiologist at the University of Toronto. “That’s been demonstrated both in laboratory studies and seen clinically in cases and hospitalizations.”
Given the high level of population immunity in the U.S. — either through infection, vaccination or both — Bogoch and others hope that, even if cases start to rise significantly, there won’t be a dramatic spike in hospitalizations or deaths as seen in previous waves.
Antibody studies don’t tell the whole story. Other parts of the immune system can protect against the virus and the Covid vaccines should remain effective at preventing severe illness and death from the virus, evidence suggests.