Influenza, a viral infection caused by influenza viruses, is a major public health problem. Each year, it affects between 2 and 6 million people in France, mainly between the months of November and April. But why does this virus seem particularly active in winter? Several factors, both environmental and behavioral, explain this seasonality.
Environmental reasons for winter flu
Winter weather conditions create a breeding ground for the survival and spread of the flu virus:
The action of cold and dry air on our mucous membranes
Low temperatures and dry air weaken respiratory mucous membranes, our first barrier against viruses. The cold alters the cells of the respiratory tract, making the tissues more permeable and making it easier for the virus to enter the body. This creates a favorable breeding ground for infection.
Ideal survival conditions for the virus
The flu virus thrives in cold, dry environments. In winter, climatic conditions allow it to survive longer, thus increasing the risks of transmission. Virologists also store strains of the virus in freezers at very low temperatures, down to -80°C, to preserve their viability.
Reduced effectiveness of the immune system
Reduced exposure to sunlight in winter decreases the production of vitamin D, a molecule essential for the proper functioning of the immune system. With weakened defenses, the body becomes less effective at fending off infections. This phenomenon also contributes to increased vulnerability to the flu virus during the cold season.
These environmental factors combined make the virus more able to spread, particularly in temperate climates, such as that of mainland France.
Winter behaviors that promote transmission
In winter, our daily habits also contribute to the spread of the virus:
Indoor life
In winter, we spend more time in enclosed, poorly ventilated spaces, such as homes, offices and public transport. These confined spaces allow virus particles to accumulate in the air or on surfaces, increasing the chances of contamination.
Social proximity
Frequent gatherings, such as holiday parties, family reunions or indoor events, promote close contact between individuals. These close interactions increase the opportunities for transmission of the virus through droplets emitted when speaking, coughing or sneezing.
-Reduction of physical activities
Cold weather and fewer hours of sunlight can discourage physical activity. However, exercise plays a key role in strengthening the immune system. A drop in activity weakens the natural defenses, making the body less resistant to pathogens.
These winter habits, although comforting, contribute to the rapid spread of the flu among the population.
Preventing the flu in winter: essential actions and vaccination
Although it is impossible to completely eliminate the risk of influenza, taking simple measures can limit its spread and reduce its severity:
Barrier gestures
- Wash your hands regularly with soap and water or a hydroalcoholic solution.
- Cough or sneeze into the crook of your elbow, and use disposable tissues.
- Ventilate the rooms daily to renew the indoor air.
- Wear a mask if you have symptoms to protect others.
Vaccination
Vaccination against influenza is the most effective way to protect yourself from severe forms. It is particularly recommended for vulnerable populations: elderly people, pregnant women, people with chronic illnesses or those who are immunocompromised. Each year, the vaccine is adjusted to match the virus strains most likely to be circulating.
The flu is most prevalent in winter due to a combination of environmental and behavioral factors. Climatic conditions favorable to the survival of the virus, a weakening of the immune system and winter lifestyle habits facilitate its transmission. Although the virus is difficult to avoid, barrier gestures and vaccination offer effective protection. By adopting these practices, it is possible to reduce the spread of the virus and limit its impact on our health.
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