Covid-19 is now ubiquitous – but hospitalisations seem to be on a downward trajectory. No one knows why.

When virologists took their first peek at XEC, the Covid-19 variant which started to become dominant in the autumn of 2024, the early signs were ominous.

The latest descendant of the Omicron variant of SARS-CoV-2, XEC had arisen through recombination, a process where two other variants had forged their genetic material together. Tests seemed to indicate that this would easily allow it to evade the immune protection offered by past infections or the latest iterations of the Covid-19 vaccines, based on the older JN.1 and KP.2 variants.

"The spike protein is quite different from previous variants, so it was quite easy to assume that XEC has the potential to evade immunity induced by JN.1 infection," says Kei Sato, a virology professor at the University of Tokyo, who carried out one of the first studies of XEC, published in December 2024.

In the US, infectious disease specialists braced themselves for an immediate surge in hospitalisations in the wake of the Thanksgiving holiday weekend. But it didn't happen. Surveillance testing carried out by measuring Covid in wastewater samples across major cities indicated that XEC was definitely infecting people. However, the numbers of people actually ending up in hospital was considerably less than previous winters. According to CDC data, the rate of hospitalisations at the start of Dec 2023 was 6.1 per 100,000 people. During the equivalent week in December 2024, that had fallen to two per 100,000 people.

"Right now, we're seeing pretty low levels of people who are critically ill, even though there's an astronomical amount of Covid in wastewater," says Peter Chin-Hong, a professor in the Health Division of Infectious Diseases at the University of California, San Francisco. "It just shows that regardless of how scary a variant might look in the lab, the environment in which it lands is much more inhospitable."

Some indications suggest that Covid in 2025 is a milder disease. The once common symptoms of loss of taste and smell are becoming less common. And though some people are being hospitalised and dying, Chin-Hong says the vast majority of people will either be asymptomatic or experience a cold so mild that some might well mistake it for a seasonal allergy, such as a pollen complaint. While immunocompromised individuals are still particularly vulnerable, he believes that the major risk factor for more severe Covid is now simply being over the age of 75.

Despite this, experts have advised that all vulnerable groups should get the latest Covid-19 vaccine, which can provide vital protection against serious illness, hospitalisation and death. And while XEC seems to cause less severe disease, there's no guarantee that more severe variants won't emerge in the future. This means the threat posed by Covid-19 is far from over and the virus should not be underestimated. Experts expect it to continue being a significant and persistent threat to public health. The risk of developing Long Covid has not gone away either. For some people, the condition can last years.

At the Icahn School of Medicine at Mount Sinai in New York, microbiology associate professor Harm Van Backel is a co-leader of the Mount Sinai Pathogen Surveillance Program, which applies the latest genomics technologies to conduct real-time tracking of bacterial, viral and fungal infections within the Mount Sinai health system. Van Backel explains that the data shows that Covid is contributing relatively little to the caseload so far this winter, despite the emergence of XEC. "For the past six months, I'd say it's been relatively quiet," he says. "In........

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