Influenza A: at the moment, duration, contagion, what is it?

After a few years of respite linked to the presence of the Covid-19 virus, the flu virus returned in December 2024. Week after week, epidemiological bulletins from Public Health France confirm the increase in flu cases, particularly among under 15 years old. Several types of influenza virus can circulate but if we are to believe the newsletter published in December Influenza subtype A predominates.

What is influenza A?

Influenza is an infectious disease caused by viruses called influenza viruses. They belong to the family Orthomyxoviridae. There are four types of influenza viruses that can cause the flu: A, B, C and D. The three types A, B and C are capable of infecting humans but only types A and B are the cause of epidemics. seasonal flu. Virus D only infects animals. “Influenza A viruses are the only ones known to cause influenza pandemics (the virus can spread throughout the world), due to their high power of propagation and low or absence of immunity against these viruses in infected people” remind her High Authority of Health. A viruses are themselves classified into subtypes or “strains” according to the characteristics of proteins present on their surface: the “hemagglutinin” (HA or H) and “neuraminidase” (NA or N) proteins. Only two subtypes of influenza A circulate in the human population: H1N1 and H3N2. They can circulate simultaneously during the same seasonal epidemic.

What symptoms? After how long?

The incubation of the influenza virus is very short, only one to two days. The virus then targets the epithelial cells of the respiratory system. It actively multiplies there and diffuses from the nasopharynx to the lower respiratory tract. It is the body’s inflammatory response that explains the sudden appearance of flu symptoms: fever (39-40°C), chills, headaches, runny nose, sore throat, cough, etc. There may also be milder forms of influenza.

How long does contagion last?

The contagion period for the flu is a good week. “The patient is contagious from incubation (so 1 to 2 days before the start of symptoms, editor’s note) and this for a period of approximately 6 days which can go up to 10 days, particularly in children. explained Dr Laurence Legout, infectious disease doctor at the Clinique du Verger in Switzerland in an article on influenza A (H1N1). The virus is transmitted by air. “The contaminated person projects droplets of saliva into the air when coughing, talking, sneezing. These droplets containing millions of viruses are found in the ambient air and will be inhaled and breathed by a non-sick person who will in turn be sick.“continues Dr Legout. Hence the importance of regularly ventilating closed spaces and wearing a mask when you are sick.

How long does influenza A last?

Elimination of the virus occurs in 7 to 10 days. The person feels better after a week but post-flu fatigue, sometimes accompanied by coughing, can last for several weeks.

What treatments?

The flu is treated with rest and paracetamol in case of fever, headaches and body aches (never aspirin, especially in children). Natural remedies can also help boost the body such as lemon juice, thyme herbal teas, diffusion of essential oils of niaouli, ravintsara or radiant eucalyptus to purify the ambient air and clear the respiratory tract.

Be careful, if the state of health worsens instead of improving over the days, you must consult or re-consult. The most common complications of the flu are respiratory: viral or bacterial pneumonia. Influenza can cause serious respiratory distress with a life-threatening prognosis. Hospitalization is necessary with the implementation of specific treatments. Smokers, the elderly, people over 45 with chronic cardiac and/or respiratory pathology, infants, pregnant women, obese people (BMI>40) or profoundly immunocompromised are most at risk of serious forms. of the flu.