As Covid Measures Are Relaxed, Old Viruses Return – And They’re Behaving Oddly

During the COVID-19 pandemic, we saw a significant decline in infections by other pathogens, perhaps most notably influenza, with the past two flu seasons being among the mildest on record. That’s because the precautions put in place to reduce the spread of COVID-19 are also effective against the flu, which is a less infectious virus to begin with. However, as COVID-19 restrictions in many countries are dismantled, viruses like influenza are coming back – but they’re not behaving in the ways we might expect.

Before anyone gets any ideas about bioweapons or (heaven forbid) 6G towers, nothing about the viruses themselves appears to have changed significantly. Rather, the way in which they’re interacting with us, their hosts, is different. Flu hospitalizations have been picking up during May – hardly peak flu season – while respiratory syncytial virus (RSV), typically a winter bug, has had large outbreaks last summer and early autumn. Adenovirus type 41, thought to cause mostly harmless gastrointestinal illness, may now be triggering severe hepatitis (liver inflammation) in healthy children.

So if the viruses haven’t changed, what has? The answer, of course, is us – or, more specifically, our immune systems. Due to covid restrictions, a smaller proportion of us have recently acquired immunity against these pathogens, which means that it’s easier for them to spread through the population and cause outbreaks under conditions that would usually make this very hard. More and larger outbreaks mean more opportunities for fringe cases to occur, such as the aforementioned adenovirus type 41 hepatitis. Some researchers think that this virus may always have been responsible for a small proportion of unexplained childhood hepatitis, but that these cases were simply too rare to make the link.

When it comes to changing virus-human interactions, lack of immunity in young children may play a particularly important role, according to experts. That’s because children are, well… germ amplifiers. Every weekday, children attend school, spend most of the day in an enclosed space mingling with dozens of other children, then return home to their families. This makes them excellent at accelerating the spread of a variety of pathogens. This means that low immunity in this group (due to extended periods of remote learning during the pandemic) has a disproportionately large effect on what we are seeing now.

Also worthy of note is that babies born during the pandemic may have weaker immunity because their mothers had fewer antibodies during gestation and following birth. Antibodies are passed from the mother to the baby in the womb and via breastfeeding, so if a mother is less exposed to pathogens during the relevant time frame, this could make her newborn more vulnerable to disease. Of course, infections during pregnancy can be a serious risk for an unborn child, so this doesn’t mean that limiting pathogen exposure during pregnancy is a bad idea – it’s just one possible explanation for why returning viruses are behaving as they are.

So, how concerned should we be about all of this? Experts are moderately worried: neither the rules of infectious disease, nor the diseases themselves, have fundamentally changed, so nothing world ending world-ending is going to happen. However, there is a possibility that we will see large outbreaks of returning diseases over the next few years. Some researchers are quite worried about what certain viruses will do when they suddenly ‘return’ to a population that has had relatively little exposure to them during the past two years. As ever, influenza is of particular concern, with some experts fearing that a buildup of people without recent exposure could lead to a very bad flu season. A good vaccination campaign will go a long way towards mitigating this risk.