What do we know about new COVID variant XBB.1.5?

A new Omicron variant XBB.1.5 is causing concerns among scientists as it is spreading like a wildfire across dozens of countries, with the UN health agency calling it the “most transmissible subvariant detected yet”.

In the United States, XBB.1.5 now accounts for more than 40 percent of COVID-19 cases, sharply rising from 2 percent in the first week of December. It is now US’s second-most dominant strain.

The XBB.1.5, which is a descendant of the Omicron XBB subvariant, has started to rise in parts of Europe, according to the World Health Organization (WHO).

Two other Omicron variants – BA.5.2 and BF.7 – were the dominant strains behind a sharp increase in COVID-19 cases in China. Beijing has said at least 60,000 people have died in the past month.

Here is what we know about XBB.1.5:

What is XBB.1.5?

XBB.1.5 is a sub-variant of the COVID-19 coronavirus Omicron strain, the most transmissible variant of concern (VOC) to date.

The spread of Omicron early last year led to record number of infections worldwide.

Unofficially named Kraken, XBB.1.5 is a sublineage of XBB –  a combination of two strains of the subvariant BA.2. It was first detected in October 2022 in the US.

XBB.1.5 has been circulating in at least 38 countries, including Canada, Australia, Kuwait, Germany and France.

Is XBB.1.5 more infectious?

On January 4, Maria Van Kerkhove, WHO’s technical lead on COVID-19, said XBB.1.5 is the “most transmissible subvariant detected yet”.

“The reasons for this are the mutations that are within this subvariant of Omicron allowing this virus to adhere to the cell and replicate easily,” she added.

SARS-CoV-2 coronavirus has continued to mutate since it emerged three years ago. Scientists have struggled to contain the coronavirus as it has constantly mutated – meaning it changed its genetic code. Mutations also meant the virus could evade immune systems and vaccines.