Harry de Quetteville

How to avoid double trouble: the difference between Covid-19 and flu

Six months ago, at the height of Covid-19’s first wave, as doctors struggled to cope with a new disease that would later kill more than a million people, there was one thing to be thankful for: spring.

Spring, in the NHS, is the season to be cheerful, the moment when the reaper – busy with winter influenza – finally packs away the scythe. But throughout 2020, with a second wave lurking, it was always a possibility that next time we might not be so lucky, that a resurgence in cases of Covid-19 might collide with flu season.

Now, it is happening. Across the country, like two viral heavyweights – the established force and the lethal newcomer – flu and Covid are about to go head-to-head for the first time. Will we be pulverised between them when they do?

Children superspread flu

Flu is, by any measure, a terrible disease. In Britain, Public Health England (PHE) put the deaths “associated with flu” at around 4,000 in the winter of 2018-19. A year earlier, however, the toll was 22,000. Why so different? The answer is that not all flu strains are the same. In 2017-18 it was the severe A (H3N2) strain that was dominant – as it had been the previous winter, when some 15,000 died. By contrast, the winter before that, 2015-16 – just as in 2013-14 – a milder strain was most prevalent, and only 7,000 or so succumbed.

Occasionally, of course, flu has the capacity to unleash a truly ghastly outlier – a pandemic. Four times in the last 100 years we have suffered such eruptions: 1918, 1957, 1968 and 2009. Each time, the problem was the same. The virus had evolved a strain that was essentially new or not seen for generations, our immune systems had no experience of it, and so we were far more vulnerable.

Many of the victims in these flu pandemics were young. In the 1958 outbreak, when an estimated nine million Britons were infected, the core sufferers were under 40. More than 100,000 children were off school in London alone and many of the adults who caught the virus got it from these youngsters. Indeed, schoolchildren, yet to assemble what the experts call an “immune repertoire” through exposure to viruses, are the original “superspreaders” – of flu at least, which is partly why it is so important that they are vaccinated. Why they are so spared by Covid remains a mystery.

How to tell if it’s Covid

Mostly, however, ordinary seasonal flu – like Covid – hits the old hardest. So is it possible to get both, even at the same time? And what are the consequences if you do?

The answer to the first question, sadly, is a very certain “yes”. Though they are both transmitted by droplets and contact, the viruses invade the body in different ways.

The result of catching both is predictably grim: according to PHE those hospital patients who contracted both diseases in the first months of this year had a 43 per cent mortality rate – compared to 23 per cent in people suffering from Covid alone.

Prof Yvonne Doyle, medical director at PHE, baldly summed up the situation: “If you get both, you are in some serious trouble.”

But Doyle added a caveat: “The people who are most likely to get both these infections may be the very people who can least afford to in terms of their own immune system or the risks of serious outcomes.” That is to say, it is not yet clear that flu will compound Covid; rather it seems that the deadly doubling of disease may target those who are already significantly susceptible.

Some symptoms, such as fever, are common to both flu and Covid. A sore throat is more common with flu, and a persistent cough with Covid. “The thing that’s really specific to Covid is the alteration to the sense of smell,” says Steven Riley, professor of infectious disease dynamics at Imperial College London. “But still, lots of Covid patients don’t get that. That’s why it is so important to get a flu jab, to lessen the chances of confusion. The fewer false positives for Covid, if flu does take off, the better. We want to avoid people spending time in hospital.”

The good news – flu might not show up at all

It is easy to feel, as winter looms, that these two viruses are ganging up against us. But, of course, they are not. Rather each is engaged on a pure, selfish, Darwinian mission to survive and replicate. And while the doubling of flu and Covid will certainly kill some, we have reason to hope that the virus overlap may actually save others.

Above all, perhaps, viruses are battling us. The global response to Covid, with its unprecedented lockdowns, mask wearing, hand sanitising, quarantines, border bans and the like, will have put not just the novel coronavirus but any virus that transmits in similar fashion, under enormous stress. The results, so far, are astonishing.

Across the southern hemisphere, which is now beginning to emerge from its flu season, 2020 saw flu almost disappear. In 2019, Australia had a particularly hard flu year, with 313,000 cases. This year there have been just 21,156 confirmed cases. But those cases all occurred before midMarch. Since the Covid pandemic, when the southern hemisphere flu season was due to get into full swing and cases normally balloon, hundreds of thousands of tests have confirmed almost total elimination of the disease. This is particularly significant because when the southern hemisphere sneezes, we in the north often catch a cold. Flu viruses often progress around the world this way. And this year, the south did not sneeze. It’s a possible silver lining to the pandemic, but it doesn’t leave room for complacency, says Riley. “We can’t be sure that there isn’t going to be a flu season here. So there’s a public health message. It’s still really important to vaccinate.”

First lines of defence

There are other knock-ons of our response to Covid-19, which might also come back to bite us. Take our newfound hygiene routines. Though it kills corona and flu viruses, handsanitiser is ineffective against other bugs. Some specialists predict our newfound reliance on sanitiser will lead to a wave of colds and winter vomiting when Covid finally takes a back seat. “Soap is still the best defence against all,” says Dr Nicky Longley, expert in infectious diseases at the London School of Hygiene and Tropical Medicine. “Hand sanitiser doesn’t work against rhinoviruses and noroviruses.”

And there are other defences, too, which we are at risk of forgetting. It seems incredible, at a moment when the whole globe appears to be waiting, with bated breath, for a Covid vaccine, that many, even in risk groups, fail to use the vaccine we do have – for flu.

Last year, flu vaccine uptake by those over 65 was only 72 per cent. For those younger, but deemed

“at risk” – with a range of health conditions like diabetes, or heart problems, or who are obese – it was only 48 per cent.

This year, it seems things will be different. “Unprecedented demand” is such that Boots has been forced to suspend its flu-jab service and some GP surgeries are reporting waiting lists of several weeks. Health Secretary Matt Hancock says that, although some countries are struggling to get supplies, Britain already has 30 million doses, which should certainly be adequate to protect the most vulnerable. Delivery to so many in a short time, however, is proving a logistical nightmare.

Riley says people should be patient and make sure they get their vaccine eventually. “There’s a lot of uncertainty about what will happen,” he says. “So we should use all the protection we have against the virus we do know well. We want schools to stay open. We don’t want to have to rely on distancing or lockdowns.”

Ultimately, however, we humans hope to do more than protect the vulnerable. For we too, adapt and modify our response to prevailing conditions. And today, around the world, we are harnessing our experiences from flu to help fight Covid – and vice versa. From the impact of obesity to the most efficient way to ventilate patients, from experimental treatments to new ways of running intensive care units, an extraordinary cross-viral fertilisation of understanding is under way.

For now, the doubling of these two grim diseases may represent “serious trouble” for us. But in the end, it may help us put the viruses themselves in a spot of bother.

The established force and lethal newcomer are to go head-tohead for the first time