XBB.1.5 Omicron Subvariant Being Closely Watched as Most Transmissible Variant Yet

XBB.1.5 is the newest Omicron subvariant that appears to be quickly taking a strong foothold in the US, making up almost a third of new COVID-19 cases nationally as of January 7, according to the Centers for Disease Prevention and Control (CDC).

In the northeast of the country, XBB.1.5 made up 72 percent of COVID infections as of last week.

The new Omicron offshoot appears to be the most transmissible variant of SARS-CoV-2 to date. It also seems to be very adept at evading the immune response owing to a plethora of mutations that makes it immune evasive.

“It is the most transmissible variant that has been detected yet,” Maria Van Kerkhove, the COVID-19 technical lead at the World Health Organization (WHO), said during a news conference last week.

The new subvariant has also been dubbed “Kraken” by some scientists.

Related: FDA Authorizes Eli Lilly’s Bebtelovimab Which Demonstrates Activity Against Omicron

White House coronavirus response coordinator Dr. Ashish Jha told that the rate at which the coronavirus is being detected in wastewater has tripled or quadrupled in many parts of the US. And most concerning is that in recent weeks, COVID-19 hospitalizations jumped by 70 percent with 300 to 400 people dying every day from COVID-19, he said.

While the XBB.1.5 Omicron subvariant is rapidly spreading across the US, it appears to remain rare in most of the world. Nonetheless, it has been found in 29 countries so far.

The good news is that there is no evidence to suggest that it causes more severe illness than other Omicron subvariants.

Importantly, preliminary data shows that bivalent COVID-19 vaccines that target the parent strain of Omicron should provide protection against XBB.1.5 and its descendants. Experts say the antiviral COVID-19 treatment Paxlovid also remains effective against infection.

There could be newer versions of XBB.1.5 on the horizon as scientists say the virus appears to be rapidly evolving, mutating faster than most viruses.

Experts also say the reason we’re seeing the continuing emergence of new variants is global vaccine inequity. They say undervaccinated regions, particularly in the southern hemisphere, continue to lack access to vaccines, resulting in the virus replicating “unchecked through an unprotected population.” This is concerning, as high-income countries are offering multiple boosters and throwing away unused vaccines.

In October, the WHO detailed that XBB.1.5 likely emerged through the genetic recombination of the Omicron BA.2.10.1 and BA.2.75 subvariants, where the two infected the same individual and swapped genetic material to create a new hybrid subvariant.

Scientists told the New York Times that most recombinant SARS-CoV-2 viruses have disappeared within a few weeks or months as they could not outcompete other lineages. However, XBB gained an advantage over the previous recombinants as it gained a set of mutations from one parent strain that helped it evade antibodies from previous infections and vaccinations. From the other parent strain, it received a separate set of mutations that made it more immune evasive.

However, while the mutations in XBB’s spike protein help prevent it from being targeted by antibodies, the mutations also lower its ability to bind host cells. This is perhaps why it hasn’t been able to readily overtake other COVID strains. However, this could rapidly change, especially in places where vaccination rates remain low. China has been experiencing a surge in COVID infections for the past couple of months, but it is unclear what version of Omicron is driving those infections due to a lack of information from the country.

Thanks to large-scale sequencing efforts, scientists in the US have been keeping a close eye on XBB. However, sequencing efforts in other parts of the world have slowed down, making it a challenge to monitor emerging and evolving forms of the virus globally.

The rise of COVID-19 infections has been a concern amid the surges of influenza and RSV in the fall and winter months, giving rise to a “tripledemic” concoction of respiratory viruses. But while the former have been easing away, COVID remains at the top of the priority list.

“We’re seeing sustained increases of COVID infections across the nation,” said Dr. Jha, which is why “COVID is the thing that concerns us most as we look at the days and weeks ahead.”