Science and health: The real reason the flu spreads in winter

Whenever summer turns to fall and leaves fall, it will appear on time. As the temperature drops and the sun fades, so does the snot. If it’s not severe, it’s just a cold that makes our throat feel like a knife has been slashed; if you’re unfortunate enough, you’ll have a high fever all over your body and pain in your extremities, which can last a week or more. This means we have the flu.

Flu season is always regular and always affects a lot of people. But even so, it’s surprising that scientists know very little about why cold weather helps the flu germs spread.

Over the past few years, however, they have finally found an answer that may help stop a widespread flu outbreak — all at the heart of how your sneeze spreads through the air.

Humanity really deserves a better understanding of influenza as soon as possible; each flu season affects up to 5 million people worldwide and kills about 250,000 of them. Part of the reason the flu is so destructive is that the flu virus mutates so quickly that our bodies are often overwhelmed by the next season’s strains.

“The antibodies in our body no longer recognize these viruses – so we lose our immunity,” said Jane Metz from the University of Bristol. It also makes it harder to develop a vaccine, and while it’s perfectly possible to design a new vaccine for every Strain, governments are often unable to convince enough people to get vaccinated.

With a better understanding of why the flu is prevalent in the winter and disappears in the summer, doctors could find simple ways to curb its spread. Previous theories have focused on our own behavior. We stay indoors longer in winter and thus come into closer contact with people who may be carrying germs.

In winter, we are also more likely to take public transport, for example – when next to a spitting passerby, when the mist from the car window gets into their cough or sneeze, we are easily exposed to flu-spreading conditions. in the tipping point.

Another popular idea focuses analysis on our physiology: cold weather can cause your body to lose its resistance to infectious diseases. The amount of vitamin D in our body may decrease due to the shortened daylight hours in winter. Since vitamin D helps strengthen our immune system, a lack of this nutrient makes us more susceptible to infectious diseases.

In addition, when breathing in cold air, the blood vessels in the nasal cavity may also constrict, avoiding the loss of heat. This potentially prevents white blood cells (fighters against germs) from reaching the nasal mucosa, preventing them from killing the viruses we inhale, allowing germs to unknowingly bypass the body’s defenses. (Perhaps that’s why it’s easy to catch a cold when we go out with wet hair.)

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While these factors all play a role in the spread of flu, the analysis shows that these theories still cannot fully explain the flu season that occurs every year. In fact, the real answer may lie in the invisible air we breathe. Due to the laws of thermodynamics, the water vapor carried by the cold air will decrease and fall as rain after reaching the “dew point”.

So, although the weather outside looks wet in winter, the air itself is drier because the humidity is lower. A series of studies over the past few years have shown that these dry conditions appear to create an excellent environment for the growth and spread of the flu virus.

For example, scientists have experimentally studied how the flu spreads between guinea pigs. In humid air, the flu virus struggles to build momentum, but in dry air, it spreads like wildfire.

After comparing the last 30 years of climate records with health records, Columbia University’s Jeffrey Shaman and his colleagues found that flu outbreaks are almost always accompanied by a drop in air humidity.

In fact, the two graphs overlap so much that “you can almost completely cover the other with one graph.” Metz recently assessed with Adam Finn for the Journal of Infection all the evidence. This finding has been validated repeatedly, including with the 2009 swine flu outbreak.

It seems counterintuitive – we often think that wet weather makes us sick rather than protects us.

To understand the reasons behind it, you need to understand the dynamics of coughing and sneezing. When we cough or sneeze because we have cold, many particles are ejected from our nose and mouth.

In moist air, these particles can be relatively large and can easily fall to the ground. But in dry air, these particles break down into smaller particles—eventually small enough to float in the air for hours, if not days. (It’s kind of like the spray you get when you turn the spray head to the thinnest setting.)

Because of this, in the winter, the air we breathe is mixed with dead cells, mucus, and viruses expelled through the respiratory tract by everyone who has recently entered the room.

In addition, water vapor in the air itself seems to pose a threat to the virus. By altering the acidity or salinity of a blob of mucus, moist air might disintegrate the surface of the virus, rendering it out of its usual weapon of attacking human cells. Viruses, by contrast, can float in dry air for hours before being inhaled into our airways and making a home in the cells of our throats.

But there are some exceptions. While the air on planes is usually dry, it doesn’t seem to increase the risk of getting the flu—perhaps because the air conditioner itself filters germs out of circulation.

And, while drier air appears to promote influenza transmission in temperate regions of Europe and North America, there are conflicting results closer to the equator, suggesting that the germs may behave slightly differently in those places.

To understand why you need to understand the dynamics of coughing and sneezing (Credit: Getty Images)

One idea is that in particularly warm and humid equatorial climates, viruses end up clinging to more surfaces indoors. So, while the flu virus doesn’t survive as easily in the air, it can survive on any surface you touch, making it more likely to get into our mouths by hand.

But at least in the northern hemisphere, these findings could devise an easy way to kill germs while they’re still floating around in the air. When Tyler Koep worked at the Mayo Clinic in Rochester, Minnesota, he once estimated that using an air humidifier in a school for just one hour could kill 30 percent of the flu virus floating in the air.

Other similar measures can be taken, such as splashing cold water on hot spots of flu transmission, such as hospital lobbies or public transportation. “This can dampen the severe flu outbreaks that occur every few years because the virus mutates,” he said. “The potential impact of an outbreak can be huge, with businesses shutting down, schools shutting down, and health being compromised.”

Sharma is experimenting further, but he believes a more delicate balancing act should be taken. “While higher humidity reduces the survival of influenza viruses, other pathogens are more active due to higher humidity,” he said. “So caution must be exercised during humidification — it’s not entirely beneficial .”

Scientists are emphasizing that vaccines and good personal hygiene are still the best ways to protect yourself; using water vapor to kill germs is just an additional front. But when you’re dealing with an enemy as cunning and ubiquitous as the flu virus, you need to use all the weapons at your disposal.