What happens when flu season and Covid collide?

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flu season
Several experts have predicted a "perfect storm" for this winter Credit: Shutterstock

WE are on the crest of the second wave of COVID-19 and if that’s not enough, we are on the verge of the annual seasonal flu season. If it is already difficult to prepare every year for a single virus, what will it be like against two, in the middle of a global pandemic?

Several experts have predicted a “perfect storm” for this winter: the synergy between SARS-CoV-2 and the influenza viruses that attack us every year could cause a very worrying scenario.

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The health services are already concentrated on fighting against Covid-19. Pushing them harder with the severity of seasonal flu (which kills 290,000 to 650,000 per year worldwide) seems like a disaster waiting to happen.

The data we have on other pandemics, such as the “Spanish Flu” of 1918-1920, suggest that the second “wave” of rebound may be much more dangerous than the first. This was caused by an outbreak of influenza virus A, of the H1N1 subtype, and in Spain alone, it ended up killing 300,000.

Are we facing a similar situation?


Although we are talking about an influenza virus, the seasonal flu is nowhere near as serious as the old “Spanish flu”, luckily. The same goes for SARS-CoV-2, although it is highly contagious.
Still, winter is coming, and with it, comes trouble.

Similarities and Differences Between Flu and COVID-19
One of the main barriers to fighting COVID-19 is found in lack of knowledge. For example, it is a virulent disease but it is difficult to detect both by asymptomatic people and due to the fact that there is no defined way to determine the appearance of the disease.


Instead, doctors use what we know about the flu, which is similar in many ways, to identify a possible person affected by SARS-CoV-2. For example, fever, headache and a dry cough, which usually occur in both COVID-19 and flu.

However, the coronavirus, according to some clinical cases, presents some symptoms of its own such as loss of smell and taste, difficulty in breathing or even the sudden and more serious worsening of symptoms.

But it must be remembered that these are not really used to detect it. Looking for these symptoms, or others, on our own is useless in detecting the infection. A test is the only thing that can reliably determine the presence of SARS-CoV-2.

What happens when two viruses meet?
Another interesting question, which we still do not know, is what happens when two viruses are in the same body. Although there are hundreds of thousands of studies with isolated viruses, there is very little research on coinfections. These occur when two pathogens infect the same tissue.

As Pablo Murcia, Professor of Integrative Virology at the University of Glasgow explains, for a virus, a human body is a gigantic environment. Talking about the mouth and the lungs are like talking about the North Pole and Patagonia. The two meeting is quite difficult, and yet it happens. This is because viruses are very specific when it comes to infecting tissues. So, they will be found in those who colonise.

And what happens then? Well, among the few pieces of evidence that exist, three types of interactions can be distinguished: positive, negative and neutral. The former causes a reinforcement in the infectious action of the viruses, unlike in the negative case, which makes them lessen. In the neutral case, they are not affected.

Among the possibilities, there may even be that “something new” arises, recombination between viruses of the same family, for example. The mechanisms behind all these phenomena are still very mysterious, although every day we are closer to unveiling them.

But not everything will be unknown. We also have some defences to overcome the winter that is to come: knowledge, prevention and vaccines. What do we know about the spread of flu viruses? For example, we know what are the factors that facilitate the circulation of influenza and other respiratory viruses: less ventilation, stay indoors, a dry environment, cold …
Anticipating and preventing the effect of these factors would help us not only to stay protected against the coronavirus but also against other respiratory diseases.

Laboratories around the world are working against the clock to find a vaccine that can counter the coronavirus.
But, the question does not stop there. Although we do not yet have a vaccine against SARS-CoV-2, what we do have is one against the flu. Keeping this disease at bay can be a key factor in not putting more pressure on the health system.

Each year, in February, the WHO publishes the composition of the vaccine that should be available in the northern hemisphere and in September that of the southern hemisphere, months before the time of flu outbreaks. This gives scope to develop the necessary vaccines that year, but there is also the probability that when the time comes, the vaccine will not be fully effective due to mutations suffered during the development period.

Still, the effectiveness of the influenza virus vaccine is estimated to be between 30 per cent at worst and 70 per cent at best. And since we do not yet have a vaccine against SARS-CoV-2, 30 per cent of a vaccine that we do have will always be better protecting us, and also reducing the severity of Covid-19 symptoms, than none at all.




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