Flu, bronchitis, bronchiolitis in children: after a calm winter thanks to barrier gestures to fight against Covid-19, seasonal epidemics return from this fall 2021. (©Illustration-Pixabay)

After more than a year and a half of the Covid-19 epidemic, we had almost forgotten them. However, influenza, bronchiolitis, bronchitis or the gastroenteritis are making a comeback at the start of fall 2021.

About the bronchiolitis, Santé Publique France (SPF) warns in its weekly bulletin published on October 6 on a “tendency to increase surveillance indicators in children under 2 years” and the transition to the pre-epidemic phase in two regions: the Grand Est and Hauts-de-France.

In adults, respiratory infections are also on the rise for a month. And the Scientific Council has just warned about the return of the flu, with an epidemic which could begin as early as October or November, “especially if the barrier measures are lightened quickly and international trade resumes”.

“This is a sign that we will not experience the dead calm of last winter, but the return of these seasonal epidemics was expected”, analyzes for his part the epidemiologist Pascal Crépey.

Here is what we know about the spread of these winter viruses and the fears they arouse.

Hospitalizations for bronchiolitis jump

Wheezing, coughing fits, fever over 39 ° C… Young children are the most exposed to bronchiolitis, a respiratory viral infection mainly caused by respiratory syncitial virus (RSV). It can cause complications in children under two years old, it is also the leading cause of pediatric hospitalization.

After a historic winter of 2020-2021 with very few hospitalizations, the trend is already completely opposite from the beginning of October. In its latest epidemiological bulletin, SPF indicates for week 39, from September 27 to October 3, a 24% increase in emergency room visits, 28% of hospitalizations and 14% of SOS Médecins interventions for this pathology.

“The speed of increase of the curves suggests that we are at the beginning of the epidemic of bronchiolitis but it is difficult to say if it will continue with this regime there”, analysis for actu.fr Pascal Crépey, epidemiologist at the School of Advanced Studies in Public Health (EHESP). Good news: the closure of schools during the school holidays, which begin on October 23, should “put a brake on it, at least temporarily, since the RSV virus spreads a lot between children”.

Immunity deficit

But what makes caregivers and scientists fear above all a “large-scale bronchiolitis epidemic” this year is the immunity deficit of children born after March 2020, who have so far not been confronted with the virus.

This immunity deficit will promote the transmission of the virus therefore potentially affecting more children and leading to more serious forms and hospitalizations in children under one year of age, the most at risk.

Hubert Crepeyepidemiologist at the School of Advanced Studies in Public Health

And besides the fact that it is very contagious, “at least as much as Covid-19”, the main difficulty posed by RSV is that there is no vaccine to date. “We must therefore try to minimize contact between infants and other children, even if we know that it is difficult in practice among siblings and depending on the type of childcare ”, advises Pascal Crépey.

Barrier gestures are receding … but certain behaviors should persist

Adults are not immune to the spread of seasonal respiratory infections. In its latest national bulletin, the network in charge of the organization of the coordinated surveillance of emergencies (OSCOUR) notes an increase, in week 39, of 22% of visits to the emergency rooms for the acute bronchitis, 13% for the pneumonia in all age groups and 10% for ENT pathologies among those aged 15 and over.

Even the gastroenteritis is gaining ground, slowly but surely: the incidence rate of acute diarrhea was 103 cases per 100,000 inhabitants in week 39, against 76 the previous week, according to the Sentinels network.

The phenomenon does not surprise the epidemiologist from Rennes: “we have almost regained the level of activities and social contacts that we had before the Covid-19 epidemic, it is not surprising that transmission is associated with it. different pathogens ”.

Yes the decline in barrier gestures observed for a few weeks can be singled out, the scientist wants to be optimistic, given that “the behavior of the population in 2021 is really different from those before the pandemic”.

Even if we are going to drop a number of protections, there are a lot of things that should remain. For example, we might think that people will be more hesitant to go to work if they have a fever, cough or will stay further away from colleagues with these kinds of symptoms. I will not be surprised either that the practice of wearing a mask is now more widespread.

Pascal Crepey

A more contagious strain of influenza already in circulation

These are all elements that should have a positive impact on future epidemics. There is still the great unknown of the immunity deficit of the population in the face of flu. In fact, there was no epidemic during the winter of 2020-2021 due to the absence of circulation of influenza viruses, both thanks to the barrier gestures and to a viral interference mechanism which means that two respiratory viruses have difficulty in co-circulating.

“Even though the predominant circulating strain of influenza virus (as a reminder there are four main strains, n.d.l.r) changes every year, we are in principle better protected if we contracted the flu the previous winter. However, this year, it is estimated that 5 to 10% of the population who should have been immunized in this way is not, ”emphasizes Pascal Crépey.

A concern to which is added that of the Scientific Council in its opinion of October 5: “The current surveillance data already show a low noise, but significant circulation of influenza viruses in Europe and in France with some circulation of A (H3N2) virus. These elements are serious signals that raise fears of an early epidemic with a significant impact on the healthcare system ”. In fact, type A (H3N2) viruses, which are more contagious, are often associated with stronger epidemics and are generally more resistant to vaccines.

Thus, the scientific council calls for a reinforced vaccination campaign, in particular towards caregivers, and to maintain reflex of the use of barrier measures.

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