Optimists had hoped Covid-19 might not withstand the blistering heat of a British summer. However those hopes have faded: the virus staged a recent resurgence in Iran amid actual blistering temperatures, and has had no trouble persisting in sultry Singapore.
But what happens to Covid-19, and us, when the rain and chill – and flu and sniffles – of autumn set in? Especially, how will the annual winter flu epidemic play out amid a Covid-19 pandemic?
One thing is a given. “We can expect waves of Covid in the fall,” says virologist Ab Osterhaus of the Research Centre for Emerging Infections and Zoonoses in Hanover. By then, he hopes, we might be better at treating severe cases, and more countries might be able to test, trace and quarantine all cases and their contacts, and contain the virus, better than they can now.
The biggest worry in the UK is that hospitals can struggle to cope with the winter flu season. This year they will have to cope with Covid-19 as well, which shows no sign of going away by then, and could even surge if it turns out that cold temperatures, or the circulation of other autumn and winter viruses, boost its spread.
The first problem will be figuring out which virus a patient has. Flu, Covid-19 and other seasonal respiratory diseases are virtually indistinguishable on the basis of symptoms, warns Barbara Rath of the University of Nottingham: even the loss of taste and smell many people get with Covid-19 is not unique. We need more and better diagnostic tests, she says, because the difference matters: medical staff need full protective gear to manage a Covid patient, but they can be vaccinated for flu.
The real unknown is what Covid-19 does around other viruses. Every autumn there is a predictable series of outbreaks of respiratory viruses. It starts with rhinovirus, the main cause of the common cold, which breaks out every September as young children go to school and swap mucus. As no parent needs to be told, children are to sniffles what mosquitoes are to malaria.
The rhinovirus subsides as most children are exposed and their immune systems activate. Then another virus breaks out: respiratory syncytial virus, or RSV. Every year in October or November, this causes mild colds in people of all ages, but sometimes severe lung infections in the youngest and oldest of us. RSV is so common that virtually all two-year-olds have already had it, and it sends more babies to hospital with pneumonia than any other virus.
Then RSV subsides, and the annual flu epidemic sets in, anywhere from early winter to spring, driven mainly by transmission among children, but taking its main toll among the elderly: some 8,000 on average die yearly of flu in the UK. This predictable parade of infections almost seems a spiteful campaign by viruses to keep people, especially families with young kids, sick for as long as possible.
But it is just a product of a little-understood phenomenon called “viral interference”: while one of these viruses holds sway in a person, or the population, for some reason the others can’t get a toehold. In September 2009, the swine flu pandemic that went on to sweep the world should have invaded Europe from the Americas. But the annual rhinovirus epidemic actually kept it at bay. The highly contagious new flu took over only when rhinovirus subsided, bumping RSV down the queue: RSV moved in only after that first wave of flu subsided.
The question now is where Covid-19 is going to fit amid this viral jostling. Not every virus takes turns like this, says Ian MacKay of the University of Queensland. Sometimes you can be infected by two at once. So which kind is Covid-19?
We do know it can infect someone alongside flu: the first Covid-19 case to die outside China was a 44-year-old man in the Philippines, who also had flu. We don’t know for sure that having flu at the same time makes Covid worse, but the fact that the Filipino victim was fairly young is worrying, says Florian Krammer of Mount Sinai School of Medicine in New York. “We assume the outcome of co-infection is not great.”
Doctors at the Tongji Hospital in Wuhan report that in January and February this year, as Covid-19 took hold in the city while flu was still circulating, many Covid-19 patients had both viruses. Co-infection didn’t seem to change their chances of survival compared to people with Covid only, but they had more heart damage, and more and earlier runaway inflammation, the over-reaction of the immune system that kills many late-stage Covid patients.
Elsewhere, however, we have had few chances to find out how often that happens. Last March, Covid-19 hit Europe as flu season was winding down, while lockdown stopped Australians from spreading flu as well as Covid and snuffed out the incipient flu season. But with little lockdown expected this autumn in the northern hemisphere, seasonal viruses and Covid will collide head-on.
If there is significant viral interference, optimists hope the child-driven autumn epidemics might keep Covid-19 at bay, as they do each other. But those viruses are transmitted mostly by children, while it appears that Covid is mostly spread by adults: the viruses might just spread in parallel, in separate populations of children and adults. That might mean more sick people in total, with severe cases competing for a fast-dwindling supply of hospital beds.
Or the fact that Covid seems to infect a different type of cell from the others might mean there is no interference, allowing co-infection with rhinovirus, RSV and flu, possibly making more people more seriously ill. “We need to hope for the best, but prepare for the worst,” says Osterhaus.
And that basically means preparing for flu, because it is the only one of these viruses for which we have a specific antiviral drug and a vaccine, despite years of intensive efforts to develop a vaccine for RSV. “That means, get your flu shot,” says Krammer.
Because flu viruses constantly evolve, though, a flu shot is something you have to get every year. Every February virologists try to predict which viruses will circulate the following winter, and companies put vaccine viruses on to grow in chicken eggs, in a process (dating from the 1940s) that takes six months.
Then those who want to avoid flu get vaccinated in the autumn just before the virus hits. If the scientists guessed right, it is at best 70% effective – but that’s better than nothing.
In the UK this is normally recommended for the pregnant, people over 65, schoolchildren and people at greater risk from flu because of underlying conditions such as diabetes, high blood pressure or lung disease – pretty much the same conditions that increase your risk from Covid-19. “This year,” says Krammer, “it should be everybody,” as Covid-19 could increase the risk for everyone.
This is partly because people who normally don’t get a flu vaccination because they are not in those high-risk groups might end up severely ill after all, because they caught Covid-19 at the same time – and of the two we can only prevent flu. Moreover, every year people who don’t officially need the flu vaccine end up in hospital anyway with some complication, typically pneumonia, that will further burden health services. Worse, they are then more likely to catch Covid-19 as well, while in hospital.
But the manufacturing process for next winter’s flu vaccine is under way and while manufacturers say they will make as many doses as possible available, they expect demand to exceed supply, as countries face a winter of flu and Covid-19. Health secretary Matt Hancock announced “the biggest flu vaccination programme in history” this week, amid reports that the NHS has bought millions more vaccine doses than the 25 million it offered last year. But it is not clear how many more will be available.
NHS England alerted doctors in May to make sure they lay in their full allotment of vaccine and make extra efforts to ensure the usual people are fully vaccinated, to take as much pressure as possible off health services next winter – although getting people vaccinated might be harder as PPE is still required for Covid-19.
The NHS is also hoping every healthcare worker will be vaccinated. But there have so far been no plans for expanding vaccination to more people, beyond calls from Labour leader Keir Starmer for free flu vaccination for everyone over 50. That is reportedly being considered, but would require 10 million more doses of vaccine.
Tamiflu, the antiviral drug that is vital for treating severe flu and saved lives in the 2009 pandemic, would also be useful to take pressure off hospitals, says Krammer. But stocks of the drug in Europe are thought to be low.
The nightmare scenario would be if this year’s flu was not the normal seasonal type, closely related to the flu we saw last year and the year before to which we all have some immunity. Every now and then a totally novel flu virus emerges that few have any immunity to – this is when flu is called pandemic. Not only would the flu vaccine we are brewing now not work against it, a new one cannot be made in much less than six months.
As for severity, the 2009 pandemic resulted in little more death than an ordinary, albeit bad, flu year – although deaths were in people in their 40s rather than people in their 80s as usual. But this was because that virus happened to be carrying surface proteins that everyone born before 1957 was immune to, as they were similar to the flu that circulated then. We needn’t be that lucky again.
Last month scientists in China warned that a swine flu there showed worrying signs of adapting to spread among people. It hasn’t yet – but that is a reminder that flu pandemics can happen any time.
The prospect of a flu pandemic hitting amid an existing Covid-19 pandemic is chilling. Death rates could be high and hospitals everywhere would be overwhelmed.
But there is, possibly, some very good news on that front. The only way around having to constantly make new vaccine for every flu season and for any pandemic flu that emerges is to develop a vaccine that works for every strain of flu, by targeting bits of the virus that all flu has in common.
Then we could be vaccinated once or twice as we are for other diseases, and remain immune regardless of what flu strikes. We could even stockpile universal vaccine if a bad pandemic strain hits and more people decide to be vaccinated.
In fact development of a “universal” flu vaccine like this has been ticking along in scientific research labs for years. But none has ever had the expensive full-blown trials of safety and effectiveness in several thousand people required to put it on the market.
That, say the researchers, is because usually only a big vaccine manufacturing company can mount such a trial. But companies must make a profit, and there has been little interest in universal flu vaccine. For one thing, it would mean replacing the current vaccine that people must buy every year with one they would need only once or a few times in their lives.
But finally the first full-blown trial of a universal vaccine candidate is happening, funded by the European Investment Bank. On 1 July Biondvax, an Israeli company, reported that it had finished tests on the 12,400 people who took its universal vaccine last year, and final results are expected by the end of the year. If they are good, says the company’s chief scientist, Tammy Ben-Yedidia, Biondvax is already geared up to make 20m doses a year, and can readily build manufacturing plants.
So we may not have this problem next year. But for Covid-19’s first real flu season this winter, we can only hope enough people get the existing vaccine to stave off trouble, for them and for healthcare systems everywhere.
Debora MacKenzie is a science journalist and the author of “Covid-19.”