Yet another new coronavirus subvariant is here: XBB.1.5. The subvariant is spreading rapidly in the United States, responsible for 41% of positive COVID-19 cases at the end of December.

"At the start of December, about 2% of cases in the US were caused by XBB.1.5. Now in early January it's probably over 50%. That is an astonishing rate of growth," Paul Hunter, an epidemiologist at the University of East Anglia, UK, told DW.

XBB.1.5 has already spread from the United States. Cases have been detected in several European countries, including the UK, Germany and France. India and Singapore have also reported cases.

"It is likely XBB.1.5 will become the dominant variant in Europe, perhaps even by the end of January. But we'll be able to manage it; there's no doubt about that," said Hunter.

XBB.1.5 transmits more easily

XBB.1.5 is a subvariant of omicron, which is currently the dominant coronavirus variant globally. XBB.1.5 is a "recombinant" subvariant of omicron, meaning it contains genetic material from different coronavirus subvariants.

"Since we first discovered XBB some months back, it's been evolving. XBB.1.5 has evolved escape mutations, meaning the virus is better at evading immunity," Hunter said.

XBB.1.5 is still neutralized by immune cells, Hunter said, but the immune system doesn't recognize it as well.

"It takes longer for the immune system to decide which antibodies to produce to stop XBB.1.5 virus particles' reproducing. That's important because how sick you get depends on how much virus is circulating in your body," said Hunter.

With a slower immune response, XBB.1.5 has more time to reproduce, increasing the likelihood of developing COVID-19 symptoms.

Is XBB.1.5 more dangerous?

Early indications in the United States suggest that XBB.1.5 is not more deadly than other omicron subvariants.

"Credible sources in the US tell us people with XBB.1.5 variant do not have more severe COVID symptoms," Hunter said.

Experts are concerned that, if XBB.1.5 spreads rapidly, the number of people with severe symptoms similar to those from other omicron subvariants will rise from sheer weight of infections.

According to Michael Head, an epidemiologist at the University of Southampton in the United Kingdom, the spread of the new subvariant comes at a bad time for health services.

"There are already high circulating levels of most respiratory viruses, including COVID-19 and influenza, this winter. There will be consequences on other areas of health [from XBB.1.5], for example routine surgery where operations will be postponed to address current health care demands," Head said.

The World Health Organization and other health institutions are keeping a close eye on infection and hospital data to track the subvariant's impact on patients.

Vaccines effective against XBB.1.5

Because XBB.1.5 is a subvariant of omicron, vaccination and/or prior COVID-19 infection will still provide systemic immunity to XBB.1.5.

"Vaccines still give us the same protection from severe COVID disease if you get XBB.1.5. However, it might be that we are slightly less protected from XBB.1.5 being transmitted," Hunter said.

According to experts, COVID-19 is here to stay, meaning that subvariants such as XBB.1.5 are likely to keep emerging.

"A high vaccination uptake is crucial to minimizing the impact of COVID-19 as a public health problem. But, in the longer term, we really do need a ‘second generation' vaccine that protects against infection and illness from all coronavirus variants," Head said.

Edited by: Carla Bleiker