This is i on Science with Clare Wilson, a subscriber-only newsletter from i. If you’d like to get this direct to your inbox, every single week, you can sign up here.

Hello, and welcome back to i’s science newsletter.

If you’re like me, you may know a few people affected by a horrible bout of Covid at the moment. So much for this virus evolving into a winter respiratory illness.

My friends have inspired me this week to dig into how bad the current variant of this virus is, as well as look at what may be behind the summer surge in cases.

The good news is that there’s no reason to think that the current Covid variants are any more dangerous than previous ones, on a population level. Although, of course, some individuals could still be having worse symptoms than the last time they encountered this virus, which I’ll get into shortly.

One thing for sure is that we are in the middle of yet another Covid wave. “There are so many cases around at the moment and some people are getting significant illness,” said Professor Peter Openshaw, a respiratory physician at Imperial College London.

The official figures confirm it too. “Our most recent surveillance report suggests that the number of hospitalisations as a result of Covid has increased slightly in the past week,” said Dr Alexander Allen of the UK Health Security Agency (UKHSA).

Nevertheless, hospital cases are still far lower than they have been at previous major peaks of this pandemic. For instance, in mid-July, there were about four admissions per 100,000 of the population in England. This is about a tenth of what they were in January 2021 – that first awful Covid winter – and there are no signs that the hospital cases are taking off.

In fact, there are early indications that cases in Scotland may have just peaked, Public Health Scotland told the BBC this week.

Fortunately, there is no sign yet that the current variants of Covid are more likely to send someone to hospital, said Professor Paul Hunter at the University of East Anglia. “There’s no evidence that it’s more virulent.”

When we have a brush with the virus, there can be a range of outcomes, from completely fighting it off, through infections that cause no or mild symptoms, to severe illness that results in hospitalisations or even deaths.

While it can be worrying to hear about people with bad symptoms, that can be unrepresentative of how most infected people are feeling, he said. “People judge severity by anecdote,” he said. “But the people that talk are the ones who feel really rough.”

Cyclical waves 

In 2024, population immunity has turned Covid into a virus that can cause an unpleasant illness, but thankfully, waves of cases do not translate into huge peaks of people needing hospital treatment or dying from the illness.

But Covid is clearly not just a winter virus, like ordinary colds and flu. So why do we keep seeing these cyclical waves of infections?

In contrast to some people’s initial hopes that vaccines or infections would be able to give “sterilising immunity” – in other words, completely block further infections – we now know that immunity to Covid isn’t all or nothing. When we are exposed to the virus, the outcome depends on many things, including our underlying health, how much virus we are exposed to and our immunity levels.

Immunity gradually wanes since we were last infected or vaccinated, but even if we do get infected (and feel miserable with it) our immunity is almost certainly cutting our chance of ending up in hospital from Covid.

Another key factor is how much the current virus has changed since the last Covid virus (or vaccine) we encountered.

New variants 

This is a key driver of waves at the population level. New virus variants are popping up all the time, and while most disappear, one arises every so often that is sufficiently different to partly overcome population immunity and start spreading.

Eventually, though, enough people have recently had Covid that it is harder for the virus to “find” new people in the population who are vulnerable– and so case numbers start falling again.

All these factors interact in complex ways that mean within a population, infection numbers tend to rise and fall in cycles.

For flu and cold viruses, the peaks almost always happen in winter. Believe it or not, we still don’t know exactly why, but it could be the fact that people tend to spend more time indoors in winter, and that colder air is drier, which helps viruses spread through the air.

It was predicted that Covid would soon settle into this seasonal pattern too, especially because it is a coronavirus, like four viruses that cause the common cold.

That clearly hasn’t yet happened. For now, because this particular coronavirus is still relatively new to our immune systems, the waning of immunity and the evolution of new variants are causing more frequent cycles, with peaks happening in summer as well as winter. “The oscillation appears to be more related to the emergence of variants rather than the seasons,” said Professor Openshaw.

But Professor Hunter believes there are signs that the winter peaks are higher than summer ones, suggesting Covid will become more of a winter virus within the next decade.

So, one answer to the question of why we are seeing a summer wave is: “Why not”? This virus is still causing regular surges, so summer is as good a time as any to have one.

But external factors could also contribute to nudging up infections, amplifying the peak. And this time, one suspect is the recent Euros championship, where many watched the matches in pubs crowded with people shouting and cheering – and breathing out lots of virus.

That might be one reason why some people are having a bad time with Covid – because when they were exposed to the virus, they breathed in a large dose of it, said Professor Hunter. “There’s no proof. But that’s a plausible explanation,” he said.

For others, it could be that it has been a long time since they last encountered the virus. Although that’s hard for anyone to know, as more than half of people infected with Covid will have no symptoms at all, according to figures from the Office for National Statistics.

In contrast to some people’s initial hopes that we might be able to eliminate Covid, most scientists now accept that people are likely to get multiple Covid infections over their lives, with varying levels of severity. But for those worried about catching Covid this summer, Professor Openshaw recommends people wear masks while using public transport. “I’m certainly trying to avoid crowded places,” he said.

The same advice goes for people with any respiratory symptoms, said Dr Allen. “We know that lots of summer activities are spent with others, but taking some time out to get better when we’re unwell helps prevent the spread of viruses and protect the people that we come into contact with, especially those who are more vulnerable.

“If you have symptoms of a respiratory virus, like a new continuous cough or fever, we continue to advise avoiding contact with others. If you do need to leave home, consider wearing a mask in crowded places.”

Other things I’ve written recently

I’m always hearing we should be aiming for eight hours of sleep a night, for mental and physical health, but it’s something that doesn’t come naturally to me.

So I was intrigued by new research that finds the benefits may have been overstated, and in fact, just six hours of sleep a night is probably fine.

I’m reading

The anti-ageing field is renowned for exaggerating the science, so I was pleased to discover Jellyfish Age Backwards: Nature’s Secrets to Longevity by Nicklas Brendborg. This is a fascinating tour of the latest longevity research that doesn’t resort to hyperbole.

This is i on Science with Clare Wilson, a subscriber-only newsletter from i. If you’d like to get this direct to your inbox, every single week, you can sign up here.