What is the 'Kraken' Covid variant XBB.1.5 spreading globally?

A new Covid variant that was first detected last year has quickly become the dominant strain in the US, picking up a creepy moniker in a nod to a mythological sea monster along the way.

Nicknamed the “Kraken variant” by some, it has surged through the nation and has now been identified in at least 28 other countries, according to the World Health Organisation (WHO).

Here are all your questions, answered:

What is the new variant?

XBB.1.5 is a descendant of the Omicron XBB sub-variant — 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 such as Singapore and India since the WHO first raised concern about it last October.

How fast is XBB.1.5 spreading?

While accounting for only 1 per cent of all Covid cases at the start of December, estimates from the US Centres for Disease Control and Prevention show 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 sub-variant which has been detected yet”, said WHO’s Covid-19 technical lead Maria Van Kerkhove during a press conference on January 4.

While only 29 countries have reported cases caused by it, health authorities are warning 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 that picture could rapidly change.

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. That means it has an ability to evade natural immunity or previous protection provided by vaccines, and reinfect people who have recovered from an earlier bout of Covid.

Data remains limited on XBB.1.5’s severity and its propensity to cause severe disease or death. Previous therapies to tackle Covid — such as monoclonal antibody treatments — were rendered ineffective by previous strains. That trend is set to continue with the new variant.

Long Covid sufferers receive oxygen therapy — in pictures

It is unclear if the US experience with XBB.1.5 will extend to other countries. America, unlike many other developed nations, suffers from low vaccination rates.

Only 15 per cent of the population aged five and above has received an updated bivalent booster dose. The rate is slightly better among the vulnerable elderly population, including those aged 65 and above, with fewer than four in 10 receiving the shot.

And hospital admission rates for Covid are already rising, amid a surge in other winter-season infections such as influenza.

The WHO plans to release an updated assessment on the variant’s risks in the coming days.

Where did the ‘Kraken’ name come from?

Covid variants are currently named by an expert group convened by the WHO. It identifies so-called variants of concern that have potential global public health significance, such as reducing the effectiveness of current pandemic measures, using the Greek alphabet.

Previous strains such as Alpha, Beta and Delta fell under the convention.

But the last Greek-named variant, Omicron, emerged more than a year ago and left no room for the emergence of other, significantly different strains. Omicron has spawned several lineages, including XBB.1.5, and their names stem from a mix of alphabets and numbers known as “Pango.”

That has led to the rise in popularity of informal online nicknames, including “Kraken”. The moniker for XBB.1.5 was proposed by an evolutionary professor on Twitter to match the strength of the new strain with the mythological sea monster.