And three. The flu signs an early start in France as hospital services operate at a tight flow, juggling between the epidemic of Covid-19 and bronchiolitis. The infectious disease appeared almost a month ahead of the winter of 2017-2018, when its circulation had already been perceived as advanced. This week, epidemiological indicators have evolved in all metropolitan areas, reports Public health France : Brittany and Normandy have gone into epidemic and six regions are in the pre-epidemic phase. By way of comparison, since the establishment of the mechanism for determining flu alert levels at the regional level (in 2015-2016), the earliest transitions to the epidemic phase only occurred from the beginning of December.
The incidence rate of consultations for flu-like illness, for example, rose by 51% over one week. This increase was particularly marked among 5-14-year-olds with regard to visits to the emergency room and hospitalizations after visits. “However, the share of hospitalizations for influenza / influenza-like illness (…) still remained this week at its basic level”, assures Public Health France. “With the co-circulation of Covid-19, there may be a certain proportion of cases for flu-like syndromes which turn out to be contaminations linked to SARS-CoV-2”, warns Sandie Munier, lecturer at Paris Cité University. and doctor of virology. However, some specialists are already sounding the alarm. At the microphone of France info Wednesday, November 23, the president of the Union of Unions of Community Pharmacists (Uspo), Pierre-Olivier Variot, predicted a “rather virulent” epidemic.
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On average, the viral infection affects between two and six million people a year in France, according to the Ministry of Health, and is responsible for around 10,000 deaths. From year to year, the virulence of influenza depends on the predominant strain in circulation. Influenza is a contagious acute respiratory infection caused by influenza viruses, whose particularity is its great genetic variability. “The virus that has an RNA genome makes a lot of mistakes when it replicates, so mutations will appear in its genome and some will be favorable to the virus. At first these mutations happen randomly. But then some will allow him to take over”, explains Sandie Munier. These small mutations placed end to end create what is called “antigenic drift”.
The flu virus is divided into three types: A, B or C. Type A or B viruses are responsible for seasonal flu, while type C is responsible for infections similar to a common cold and which go unnoticed . “Type A viruses can cause new pandemics, because many subtypes against which the human population has no pre-existing immunity are present in a large number of animals (especially poultry)”, decrypts Sandie Munier. For its part, the type C virus is rarely detected. This year, the influenza viruses identified in metropolitan France are mainly of subtype A (H3N2), “often responsible for slightly more severe influenza than H1N1 influenza”, adds Sandie Munier, adding that the predominant variant may evolve in the coming weeks. “Seasonal flu affects a much wider panel in terms of serious form, children also represent a population at risk”, says Yves Coppieters, epidemiologist at the Free University of Brussels (Belgium).
A suitable vaccine
Will the vaccine currently on the market be sufficiently suitable? “It should protect well against the different strains that are currently circulating,” reassures the virologist. Indeed, the flu vaccine is “quadrivalent”, that is to say that it contains four different strains of the flu virus. It protects against two strains of influenza A and two strains of type B. “Each year, the vaccine is updated so as to be as close as possible to the strains that circulate. The World Health Organization (WHO) decides of the vaccine composition in February for the northern hemisphere so that the vaccine can be put on sale in November”, explains Sandie Munier. Its composition for the 2022-2023 season in northern latitudes is defined from the monitoring of viral strains in circulation during the last season in the southern hemisphere.
But many bottles are still waiting to find a buyer, the population concerned (frail, elderly, immunocompromised) not rushing to the places of vaccination. A little over a month after the launch of the vaccination campaign, around 7.5 million doses had been distributed on Tuesday, November 22, against 9.4 million last year at the same stage. “You have to wait a fortnight for immunity to set in after vaccination. There are people who can receive their injection now, but there is a risk of catching the flu before being fully immunized”, warns Sandie Munier. Like Covid-19, influenza viruses enter the body through the respiratory route. They are transmitted “by droplets and aerosols emitted by an infected person when he coughs, sneezes, speaks, sings or breathes”, specifies the WHO.
Viruses can also be exchanged through the hands when an individual is in contact with a contaminated surface and brings his hand close to the nose. This is why the health authorities recommend barrier measures during epidemics (wearing a mask in public places, hand washing). “For seasonal flu, transmission by hands has been well demonstrated, which is not the case with Covid-19”, indicates Yves Coppieters. The time between contamination and the appearance of symptoms (incubation period) is one to three days on average, and can be up to five. During this time, the infected person can transmit the virus. “You continue to be highly contagious during the first days, up to six days after the onset of symptoms”, underlines Yves Coppieters, specifying that there are also little symptomatic or asymptomatic forms.
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Regarding the symptoms of the flu, they are similar to those described for Covid-19: cough, fever, throat irritation, headache. The coronavirus is distinguished from the flu by other more specific symptoms: extreme fatigue, unusual shortness of breath and loss of taste and smell which appears in a third of situations. In order to make the correct diagnosis, the best way is to carry out a screening test for Covid-19. But the current dual circulation of the coronavirus and flu epidemics is worrying on several levels. “It is possible to make a co-infection, which can worsen the prognosis for fragile populations and also threaten to saturate hospital services”, warns Yves Coppieters.
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