New COVID-19 strain is the most transmissible yet, says WHO 

The new coronavirus strain, Omicron’s XBB.1.5, is rapidly spreading throughout the world, raising concerns that it could drive up cases, a World Health Organization (WHO) official told reporters on Wednesday. 

“We are concerned about its growth advantage, in particular in some countries in Europe and the Northeast part of the United States, where XBB.1.5 has rapidly replaced other circulating sub-variants,” said Maria Van Kerkhove, the WHO’s Covid-19 technical lead.

“Our concern is how transmissible it is, … and the more this virus circulates, the more opportunities it will have to change,” she added.

XBB.1.5 has been detected in 29 countries so far, the WHO added. In the United States, the new subvariant is making up more than 40% of the coronavirus cases in a matter of weeks, according to White House COVID-19 Response Coordinator Ashish Jha. In the northeastern part of the country, 75% of the confirmed cases are reported to be of the new strain. 

Good morning

Over the holidays, you may have heard about Omicron XBB.1.5

It went from 4% of sequences to 40% in just a few weeks

That’s a stunning increase

So what does it mean? Will it cause a wave of serious illness and death?

Here's what we know, don't know

🧵

— Ashish K. Jha, MD, MPH (@AshishKJha46) January 4, 2023

The WHO, however, does not yet know whether XBB.1.5 is more severe than other COVID-19 sub-variants. 

“XBB15 may be more transmissible than other variants, but we don’t know if it causes more severe disease,” the Centers for Disease Control and Prevention (CDC) said. 

Additionally, health officials do not yet know how the new strain will affect individuals who are vaccinated or have had a prior infection. 

Jha, however, warned that immunity against XBB.1.5 “is probably not great” if someone was infected before July or has not received the bivalent booster. 

The WHO is working on an analysis of the new strain, hoping to publish its findings in the coming days, Kerkhove said.