Should we expect a fifth wave of coronavirus this fall?

• Autumn, with the accompanying drop in temperatures, is conducive to the spread of Covid-19.

• And with a more contagious Delta variant, which represents almost all of the new cases detected, a fifth wave could arrive as early as the next few weeks.

• The significant vaccination coverage, even if it has not yet made it possible to achieve collective immunity, should however make it possible to avoid overwhelming hospitals.

"The epidemic decline continues day after day", welcomed this Wednesday the spokesman of the government, Gabriel Attal, announcing in passing some relaxation of health measures at the end of the Defense Council.

But while the fourth wave falls back in France, is a fifth already in ambush?

If the figures for contamination and hospitalizations linked to Covid-19 are constantly falling, doctors and scientists are already warning that a next epidemic rebound is to be expected in the fall.

How big could this fifth wave be?

Which populations could be infected and with which forms of the disease?

And how will this coming wave be different from the previous ones?

"The conditions are right for us to have a fifth, or even a sixth wave"

“With the arrival of autumn and winter, temperatures drop, we live more indoors and we ventilate less. And faced with a virus that diffuses so well with the Delta variant, the conditions are met for a fifth, or even a sixth wave, estimates Dr. Benjamin Davido, infectious disease specialist at the Raymond-Poincaré hospital in Garches (Hauts -de-Seine). Especially since to date, only 64% of the population has been vaccinated, so we have not achieved collective immunity which could prevent a restart ”. However, “unvaccinated adults contribute significantly to pressure on the hospital (…) and disproportionately to transmission,” recalls the Institut Pasteur in its latest model of the epidemic. In our baseline scenario, unvaccinated people over the age of 60 represent 3% of the population,but 43% of hospitalizations ”.

For Professor Arnaud Fontanet, epidemiologist at the Institut Pasteur and member of the Scientific Council, the arrival of a fifth wave in the fall is therefore not a shadow of a doubt: “There is a reservoir of population. in which the virus can circulate: these are children under 12, since they are not vaccinated, and unvaccinated adults: we know that among those over 80, there are still 15% of unvaccinated ".

However, "from October 4, in the departments where the incidence rate stabilizes below the threshold of 50 per 100,000 inhabitants, (...) the obligation to wear a mask in primary school will be lifted", said Gabriel Attal.

Before adding, however, that "the health pass continues to apply under the same conditions as today".

Contaminations to be expected in vaccinated people

So who is at risk of being infected during this fifth wave? "We expect that a third of infections will take place in children and adolescents," say modelers at the Institut Pasteur. And as "with the Delta variant, vaccinated people are less well protected against infection (although protection remains very high against severe forms), they recall, we expect about half infections occur in vaccinated people ”. How to explain it? First for an arithmetical reason: "the more the population is vaccinated, the more the proportion of vaccinated among the cases increases", reassures the Pasteur Institute.

Another reason: Public Health France observes, in its latest bulletin, a "decline in the adoption of all barrier gestures since the end of June". “When you are vaccinated, you are five times less likely to be infected, and ten times less likely to be hospitalized for a severe form. In fact, you relax on the barrier gestures, and it is precisely this decline that will fuel this fifth, even this sixth wave, ”explains Dr. Davido. "It is therefore important that the vaccinated people continue to respect the barrier gestures and to wear a mask", insists the Pasteur Institute. "All the more so as the next vacation will lead to a mixing of populations across the territory, and it is not known whether by then a new variant will not have appeared", adds Dr Davido.

In addition, "we must not forget that from October 15, screening tests" comfort "will no longer be reimbursed, notes Dr. Davido, while many are screened as part of the health pass.

However, if we detect less, the virus will evolve in a less visible way, at a period known to be the season of respiratory viral diseases ”.

"An epidemic wave yes, but not necessarily a hospital wave"

However, the scenario envisaged for this fifth wave does not foresee a health disaster. “With the foreseeable increase in contamination among vaccinated people - who will develop attenuated forms of the coronavirus and be superimmunized against it - we will have a population that is better protected even against variants that could appear. Their individual immunity will strengthen collective immunity by protecting others, ”explains Dr Davido. For the infectious disease specialist, this particularity means that "the term" wave "is overused, since it implies the notion of submersion of the hospital system. If the vaccine does not prevent epidemic waves, its effectiveness against severe forms is such that the next rebounds should not necessarily be accompanied by a hospital wave ”.

An enthusiasm shared by Dr Fontanet.

"The very good news is that 80 to 90% of the adult population is immune, so the measures that we will have to take to slow down this next wave will not be of the same magnitude at all," he said. he assured on LCI, sweeping aside the hypothesis of a reconfinement or a return of the curfew.

“I'm not particularly worried about the coming fall,” he added.

But if the indicators are rather reassuring in metropolitan France, the wave that has been sweeping for several weeks in the West Indies and New Caledonia is not over.

At issue: a much lower vaccination rate, which has led to saturation of hospitals.

"It is essential that the vaccination coverage in the most vulnerable be as high as possible", insists the Pasteur Institute.

Finally, the intensity of the next wave should also "depend on the effectiveness of the third dose campaign, to prevent the very first vaccinated from being - because of the decline in their immunity - the first to develop serious forms. ".

But the end of the year could also bring good news, "with the expected arrival of new anti-Covid vaccines, advances the infectious disease specialist, which could fuel this recall campaign".

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