Why the flu epidemic is starting again in France

After an initial increase in the number of cases at the end of 2021, flu infections in France have been increasing again for a few days.

Public Health France notes in its latest weekly bulletin a “sharp rise in all flu indicators” in France. After an initial increase in the number of cases at the end of 2021, a second flu wave is on the way, which can be explained by several factors.

“After a first epidemic wave that occurred from S51-2021” [du 20 au 26 décembre 2021]Île-de-France had moved to a post-epidemic level in S03-2022 [du 17 janvier au 23 janvier] and go back to S10 [du 7 mars au 13 mars] in an epidemic,” explains Public Health France.

There was almost no flu epidemic during the winter season 2020-2021 and the curve for this season remains low for now and does not resemble the usual abrupt spikes seen for the 2018-2019 or 2017-2018 season.

Weekly evolution of flu hospital admissions in metropolitan France over several years
Weekly evolution of flu hospital admissions in metropolitan France over several years © Santé Publique France

The relaxation of barrier gestures pointed out

For Jérôme Marty, General Practitioner, President of the French Union of Free Medicine, this increase in the number of cases is clearly due to the relaxation of barrier gestures following the lifting of health restrictions.

“If we’ve had no or almost no flu epidemic in nearly two years, it’s thanks to masks and hand washing,” he reminds BFMTV.com. But with the lifting of many restrictions, “people are clearly relaxing, and that has led to a renewed acceleration of the flu epidemic,” for him.

In fact, for Santé Publique France, the intensification of the flu is partly due to “the current easing of measures to control the Covid-19 pandemic”.

A harmful effect of the start of the school year

This increase was also “favored towards the end of the winter school holidays in all regions,” SPF writes, as the mixing of schoolchildren at school is known to be a vector for the spread of disease. The increase in the number of flu cases follows the different back-to-school periods in February according to the holiday zones.

“I already mentioned that with the start of the school year we risked a resumption of Covid-19, we see the same with the flu,” says BFMTV.com infectious disease specialist Benjamin Davido.

· Poor immunity?

Faced with the flu, as with Covid-19, it is the elderly who are most at risk because they have a more fragile immune system. And their body was not or hardly ever confronted with the virus last year, which has prevented it from training to fight the infection.

In addition, even if a vaccination call was launched in the fall for Covid-19 and flu, it was “done in October or November”, underlined with the Parisian Bruno Lina, virologist and member of the Scientific Council. And the further we move away from vaccination, the more “we lose vaccine efficacy,” he explains.

The effectiveness of this year’s flu vaccine is still unknown anyway, “the first estimates of the real-life effectiveness of the flu vaccine will be communicated as soon as they are available,” writes SPF.

Virus competition could play against the flu

On the other hand, this increase in flu cases comes at a time when Covid-19 cases have also started to rise again in recent days, and the coexistence of the two viruses could work against SARS-CoV-2, says Benjamin Davido. “Viruses find it difficult to co-exist at the same time, it is possible that this competes with Covid-19,” he explains.

“Because the virus is less important, leave the flu [autre appellation de la grippe] the possibility of recirculation and we are witnessing the real onset of a flu epidemic,” explains Bruno Lina.

An increase in the number of cases that could stop

This onset of the epidemic’s resumption is late compared to previous years where they ended rather than started at this time of year. Benjamin Davido also notes that “the last peaks we could have were in week 9”, ie the first week of March. In that sense, for him, with the arrival of spring and more favorable atmospheric conditions, “the flu could go down again in April,” like other respiratory infections.

For example, Health Minister Olivier Véran assured France Info on Wednesday that the Covid-19 epidemic “would probably increase for 10 to 15 days, until the end of March (…) and then we expect a decrease”.

Santé Publique France recalls that in order to protect itself against the flu and its complications, “the systematic introduction of barrier movements and anti-flu vaccination should be considered effective means”.

Salome Vincenton

Salome Vincenton BFMTV journalist