Why does the flu become more active during the cold season?
Last reviewed: 15.08.2021
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Every fall and winter we have to remember about the flu and ARVI. Why is there epidemics at this time of year?
Strange, but still seven or eight years ago, scientists had no idea why the spread of viral infections becomes more active with a cold snap. Now science has found the answer: it turned out that the whole point lies in the drip transfer of infection.
If you recall the laws of thermodynamics, it turns out that the relative humidity of cool air is less than warm. Thus, reaching the dew point, when wet steam falls as precipitation, the concentration of steam in the cool air will be less than in the warm. In practice it looks like this: it rains in the yard with snow, but the air is drier at this time than in the warm season.
Additional studies have confirmed that dry air is a more favorable habitat for the virus, in contrast to high humidity conditions.
Therefore, the epidemics of viral diseases in the vast majority of cases are observed against the background of a decrease in the relative humidity.
How does this happen visually? When coughing or sneezing from the respiratory system, there is a sharp release of the droplet suspension. In moist air, these droplets coalesce and settle to the ground. If the air is dry, the droplet slurry splits into minute particles that do not settle, but continue to "float" in the air for hours or days. Because of this, we have every chance to breathe an invisible infection, which was released into the air by a sick and coughing man, even if he coughed yesterday.
There are other factors that contribute to the incidence of influenza in the cold season. Viruses enter the body mainly through the mucosa of the upper respiratory tract. However, the nasal cavity is constantly produced protective mucus, which "catches" the infection and immobilizes it. In the future, these discharges are lowered into the nasopharynx, and we swallow them unnoticed. If the air is cold, then the mucus freezes, and its excretion slows down. As a result, viruses that are "stuck" in mucus are permanently retained on the mucosa, where they have the ability to multiply and reduce local immunity. This can also be explained by the fact that doctors advise in the cold season to wash the nasal canals with isotonic solution - in order to mechanically wash out "stuck" viruses and microbes.
An additional negative role in the development of the epidemic is also played by the fact that in the cold season our immune defense weakens, a lack of vitamins occurs, in particular, stocks of vitamin D are running low.
Is it possible to protect yourself and your loved ones from a viral invasion? Of course you can! And everyone knows about these methods of protection: you need to wash your hands frequently with detergent, do not touch unwashed hands with your face, avoid accumulation of a large number of people, and make changes in food - to supply the body with enough vitamins. No less important are also regular humidification of premises, ventilation. As an aid, seasonal vaccination can be used.
The full version of the article is available on the BBC Future website.