“Covid-19 is now ubiquitous – but hospitalisations seem to be on a downward trajectory. No one knows why.
"'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.'
Even when patients are admitted to hospital, the treatment protocols have changed markedly in the last two to three years. Chin-Hong recalls that anticoagulants or blood thinning medications would immediately be administered to lower the chances of clotting, but this is now no longer considered necessary. While steroids such as dexamethasone are still used in certain severe cases, he says that these tend to be exceptions, with antivirals being the predominant treatment needed.
'I think Omicron and its subvariants have increasingly focused more on causing milder upper respiratory cold symptoms rather than pneumonia and some of the invasive manifestations we've seen in the past like cardiovascular disease and clotting,' says Chin-Hong. 'It means that when people come into hospital, they tend to be in and out in a shorter period of time.'
As part of his work tracking various respiratory viruses at the University of Missouri School of Medicine, the molecular virologist Marc Johnson uses all kinds of avenues to examine the levels of Covid currently circulating. Just like Chin-Hong, he can confirm that there is plenty of it around.
'We started doing air sampling at a lot of sites around the university, and it's pretty rare that we could pull out a sample from around the students and not detect Covid,' he says. 'We're still getting exposed all the time, but most infections are probably just getting blunted.'
But it hasn't been easy to deduce why. Sato explains that one of the reasons that new Covid variants often seem far scarier than they actually are, is because their virulence is typically tested by injecting them into hamsters. 'But of course hamsters have not been vaccinated,' he says. 'Hamsters are very similar to the humans of 2019. They have no specific anti-SARS-CoV-2 immunity, so the situation with the humans of 2025 is quite different.'
'Even if Covid gets in, right now it's going to be identified and kicked out of the body pretty efficiently,' says Chin-Hong. 'Most of the time, it's not lingering around long enough to cause serious disease, or chronic problems. With long Covid, one of the hypotheses is that the virus is triggering this aberrant immune response, but if it's not able to stick around as long anymore, there's less risk of that happening,' he says.
'People often look to influenza pandemics like the 1918 Spanish flu for clues as to what might happen with Covid, but coronaviruses may be inherently different from influenza, and so coronaviruses of the past may give better clues for the future,' says Chin-Hong. 'Overall, it seems that we may see less invasive disease and long Covid over time as population immunity improves, despite the continued evolution of the virus to create variants like XEC that look scary in the lab.'
However, Johnson says that if an immunocompromised individual was to now be infected with an older strain of Covid such as the Delta variant from 2020, it could lead to something radically different. He believes this could have a more drastic impact in terms of illness and hospitalisations as it would look completely foreign to our body.
It's also plausible that something even stranger might unfold. According to Johnson, there are some early signs that Covid's eventual trajectory could lead it to become a faecal-oral virus, more akin to norovirus, cholera or hepatitis A than the common cold.
Johnson's hunch is that this occasionally happens because a strain of Covid has acquired mutations which allow it to become a persistent gastrointestinal infection. As a result, he believes it is plausible that SARS-CoV-2 could eventually find a way of being spread via stool particles, just like other faecal-oral viruses.
'A lot of the bat coronaviruses, that's how they spread,' says Johnson. 'Interestingly, the evolutionary ancestors of Covid were not respiratory viruses, they were enteric viruses [those that live in the gut], spread via faecal-oral routes such as contaminated food, water or interpersonal contact. So it's possible that Covid could become an entirely food-borne pathogen, but that's probably not happening any time soon.'
The other key question is the potential consequences of having a longer-term Covid gastrointestinal infection and how common this is. To try and find out more, Johnson is now attempting to recruit people who have experienced long-term gastrointestinal problems in the aftermath of an acute Covid infection, for a study.
Johnson believes it is particularly important for public health to try and understand some of the consequences of long-term Covid gut infections. He's noticed that after a period of time, sometimes many years, most of the cryptic lineages he spots repeatedly in wastewater ultimately disappear. 'My guess is that the person dies, but I don't know that for sure or why,' he says. 'There's a lot of unanswered questions.'
'At the end of the day, what happens next with Covid is still somewhat unpredictable,' says Chin-Hong. 'While there is still some risk of severe illness and hospitalisation, we still need better therapeutics and vaccines, for some people at least in the future.'"