What impact could Covid-19 have on the future flu epidemic?

Lille, October 22, 2018. Illustration vaccine against the seasonal influenza virus.

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• As the number of Covid-19 cases continues to rise, the Department of Health and some doctors are questioning the impact the pandemic could have on the flu epidemic.

• In general, the flu, which affects the same public as the coronavirus, kills between 10,000 and 15,000 and puts stress on hospitals and doctors' offices.

  A double wave would therefore be very difficult to manage for our health system.

• But if the barrier gestures, which are the same for the Covid-19 as for the flu, remain highly respected, it is also possible that the next flu epidemic will be less severe than in previous years.

Fever, severe fatigue, cough: Flu or Covid-19?

While the upcoming entry into the fall promises us the usual panoply of pathologies and that the Covid-19 has not finished its tour of France, should we fear a stacking of epidemics?

Or, on the contrary, hope that this new disease will limit the damage caused by the flu?

Hope from the southern hemisphere

"The answer is that we do not know, carefully slice William Dab, epidemiologist and former director general of health (DGS) from 2003 to 2005. We have some clues that come to us from the southern hemisphere, where c t is winter, but it won't necessarily be like that here.

Indeed, several studies have shown that the flu epidemic is minimal.

Especially in Hong Kong, where the 2019-2020 version of the flu is both shorter than the previous five and less fatal, an article in the journal

.

More generally, according to the WHO influenza surveillance data, the epidemic ended in early April, while it usually continues until the end of May in the southern hemisphere.

“According to WHO figures, in the last week of August, out of two million patient samples, 40 influenza viruses were detected, it is ridiculous, analyzes Bruno Lina, virologist and member of the Covid Scientific Council- 19.

Last year, at the same time, out of 50,000 samples over a week, there were 5,000 viruses detected.

"

Not two epidemics at the same time?

How to explain this?

"It's difficult to talk about a positive effect of this Covid-19 epidemic," continues Bruno Lina.

Nevertheless, some imagine that it could "block" the circulation of the flu.

“Respiratory viruses have trouble circulating at the same time when they target the same patient profile,” he explains.

In a normal year, there are sequences of epidemics: first rhinoviruses from September to November, then bronchiolitis until December and from January to March, influenza.

They substitute for each other, because when you are infected you develop interferon, a non-specific immune response, which lowers the risk of being infected with another pathogen.

We could therefore imagine that if the coronavirus circulates in abundance, it will limit the existence of others.

"

The other good news is that the French have adopted prevention reflexes in a very short time.

"It is certain that the adoption of barrier measures reduced the epidemic of influenza and gastroenteritis last year," suggests Frédéric Le Guillou, pulmonologist and president of the Association Santé Respiratoire France.

"Masks, distancing, hydroalcoholic gel, all of these anti-Covid measures are formidably effective against other respiratory viruses," continues Bruno Lina.

The coronavirus had an R0 around 3 and thanks to the barrier measures, this R0 fell to 1.5.

So when you have viruses that naturally have an R0 of 1.5, we go below 1 and there is no epidemic.

It is possible that between all the barrier measures (if they continue to be respected), and the flu vaccination campaign, there will be a total absence of circulation of the flu virus this year.

It is the first time that I say that and it is thirty years that I work on the influenza virus.

So much for the idyllic scenario ...

System overwhelmed by a series of epidemics

There remains a much darker hypothesis.

That of a second wave of coronavirus (the DGS report of September 3 shows 7,000 new cases in 24 hours), concomitant or followed by a severe flu epidemic (which affects on average in France between 2 to 8 million people and causes between 10,000 and 15,000 deaths per year).

We let you do the math and imagine the overwhelmed city offices and hospitals ...

“One of the problems is that the clinical symptoms are almost indistinguishable, except for the sudden loss of smell and taste,” says Frédéric Le Guillou.

The tests will allow us to make the difference.

Hence the importance of being able to test on a large scale.

“The issue is logistics,” continues the pulmonologist.

In winter, if there is an influx of flu patients and coronavirus patients, the health system may not resist.

Without forgetting the collateral damage… While we take care of these patients, resuscitation, the Samu cannot take care of infarcts, epilepsies, of all the other patients.

"

"If there was a strong influenza epidemic, given that the symptoms are similar, it would complicate epidemic surveillance," adds William Dab.

Epidemiologists, statisticians, but also researchers, very mobilized for months on the Covid-19, would therefore find it difficult to follow closely, continue their work and distinguish these two epidemics.

"This catastrophic scenario is not necessarily the most likely, but to say that it will not happen is not reasonable", synthesizes Bruno Lina, virologist.

A risk that has not escaped the Ministry of Health, vigilant on this issue.

"We anticipate a blurring of the lines and we pay particular attention to the vaccination of the elderly", we are told at the cabinet of Olivier Véran.

Call for vaccination

A call for vaccination relayed by many doctors.

The Haute Autorité de Santé published a recommendation in June 2020, insisting on the importance of improving vaccination coverage: in 2019-2020, only 45% of people over 65 had been vaccinated.

Despite targeted campaigns, an invitation by Social Security to get vaccinated for free and directly from your pharmacist ... "There is also a reflection to be carried out on the vaccination of caregivers, doctors and paramedics", insists Frédéric Le Guillou, who regrets the reluctance of some who risk contaminating their patients involuntarily.

"Even if it should be kept in mind that the vaccine only partially protects against the flu", nuance William Dab.

In fact, the effectiveness of the vaccine is generally around 70-75%, but may vary from year to year.

Nevertheless, some want in this context of an unprecedented pandemic, pharmacists can vaccinate the entire population, and not only those over 65 and chronically ill.

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