NEW YORK – A new coronavirus subvariant that was first detected in 2022 has quickly become the dominant strain in the United States, picking up a creepy moniker along the way.

Nicknamed the “Kraken” variant by some, it surged through the nation and has now been identified in at least 31 other countries, according to the World Health Organisation (WHO).

Is it more dangerous? Does it spread more easily? And how will it affect China’s Covid-19 outbreak? Here are the answers:

What is the new variant?

XBB.1.5 is a descendant of the Omicron XBB subvariant, which is itself a cross between two earlier strains: BA.2.75 and BA.2.10.1.

The original XBB variant has already caused waves of infection in countries including Singapore and India, since the WHO first raised concern about it last October.

How fast is XBB.1.5 spreading?

While accounting for just 1 per cent of all Covid-19 cases at the start of December, estimates from the US Centres for Disease Control and Prevention showed that it surged to become the dominant strain by the end of the month, responsible for about 41 per cent of all infections. In north-eastern states, that figure has jumped above 70 per cent.

XBB.1.5 is “the most transmissible subvariant that has been detected yet”, said the WHO’s Covid-19 technical lead, Dr Maria Van Kerkhove, during a press conference on Jan 4.

While only 31 countries have reported cases caused by it, the health authorities are warning that it could be much more widespread and silently proliferating thanks to a drop-off in testing.

In other countries, the proportion of infections caused by XBB.1.5 has remained lower, although the picture may rapidly change.

Estimates from the Wellcome Sanger Institute found that the variant made up around 4 per cent of Covid-19 infections in England as at mid-December, while Canada has found a handful of such cases.

Scientists pointed out that the sub-variant has a much stronger affinity to ACE2, a key receptor for the virus, which allows it to bind more easily and boosts its transmissibility.

Is it more dangerous than previous variants?

There have not been significant differences in severity reported between cases caused by XBB.1.5 and previous variants.

Like other strains that concerned scientists, however, XBB.1.5 is attracting attention because it is exhibiting signs of immunity escape. This means it has an ability to evade natural immunity or previous protection provided by vaccines, and re-infect people who have recovered from an earlier bout of Covid-19.