Why cold and flu viruses are more common in winter

Editor’s note: Get inspired with our weekly roundup on the good life, made easy. Sign up for CNN life but better A newsletter with information and tools designed to improve your wellbeing.


There’s a chill in the air, and you all know what that means—it’s cold and flu season, and it seems like everyone you know is suddenly sneezing, runny nose, or worse. It’s as if those pesky cold and flu germs hit with the first wave of winter weather.

However, germs are present year-round—think back to when you caught a cold last summer. So why do people get more colds, flu and now Covid-19 when it’s cold outside?

In what researchers call a scientific breakthrough, the scientists behind a new study may have found the biological reason why we get more respiratory illnesses in winter. It turns out that the cold air itself can impair the immune response that occurs in the nose.

“This is the first time we have a biological and molecular explanation for a factor of our innate immune response that appears to be limited by cooler temperatures,” said rhinologist Dr. Zara Patel, professor of otolaryngology and head and neck surgery at the Stanford University School of Medicine in California. She was not involved in the new study.

In fact, lowering the temperature inside the nose by 9 degrees Fahrenheit (5 degrees Celsius) killed nearly 50 percent of the billions of virus- and bacterial-fighting cells in the nostrils, according to research published Tuesday in the Journal of Allergy. Immunology.

“Cold air is associated with increased viral infections because with just a small drop in temperature, you basically lose half your immunity,” says rhinologist Dr. Benjamin Bleier is Chief of the Otolaryngology Department at Massachusetts Eye and Ear Infirmary and an Associate Professor at Harvard Medical School in Boston.

“It’s important to remember that these are in vitro studies, which means that while it’s using human tissue in the lab to study this immune response, it’s not a study that’s been done inside someone’s actual nose, ’” Patel said in an email. “Findings from in vitro studies are often, but not always, confirmed in vivo.”

To understand why this happened, Bleier and his team, along with co-authors Mansur Amiji, The head of the Department of Pharmacy at Northeastern University in Boston, continues the scientific sleuthing.

Respiratory viruses or bacteria invade the nose, which is the main entry point into the body. The team found that bacteria were detected in the front of the nose immediately before intruders were detected in the back of the nose.

At that point, the cells lining the nose immediately begin producing billions of simple copies of themselves, called extracellular vesicles, or EVs.

“EVs can’t divide like cells, but they’re like tiny cells that are specifically designed to kill these viruses,” Bleier said. “The EVs act as baits, so now when you inhale the virus, the virus sticks to those baits, not to the cells.”

Those “mini-me” are then expelled by cells into the nasal mucus (yes, snot) where they stop Invading bacteria before they reach their destination and multiply.

“It’s the part, if not the only part, of the immune system that allows your body to fight bacteria and viruses before they actually enter your body,” Blair said.

Once produced and dispersed in nasal secretions, billions of EVs begin swarming, Bleier said.

“It’s like if you kick a hornet’s nest, what happens? You might see a couple of hornets flying around, but when you kick it, they all fly out of the nest before the animal can get in.” attack,” he said. “That’s how the body clears these inhaled viruses so they never get into cells in the first place.”

The study found that when challenged, the nose increased production of extracellular vesicles by 160%. There are other differences: EVs have far more surface receptors than protocells, thus enhancing the virus-blocking capacity of the billions of extracellular vesicles in the nose.

“Think of the receptors as little arms outstretched, trying to grab viral particles as you inhale them,” Blair said. “And we found a 20-fold increase in the number of receptors on the surface of each vesicle, making them super sticky.”

Cells in the body also contain virus killers called microRNAs, which attack invading bacteria. However, the study found that EVs in the nose contained 13 times more microRNA sequences than normal cells.

So the nose comes into battle with some extra superpowers. But what happens to those advantages when cold weather hits?

To find out, Bleier and his team exposed four study participants to temperatures of 40 degrees Fahrenheit (4.4 degrees Celsius) for 15 minutes and then measured what was going on inside their nasal passages.

“We found that when you’re exposed to cold air, the temperature in your nose drops by as much as 9 degrees Fahrenheit. That’s enough to essentially eliminate all three immune advantages that the nose has,” Blair said.

In fact, a little cold on the tip of the nose was enough to stop nearly 42 percent of the extracellular vesicles from fighting, Bleier said.

“Similarly, the number of killer microRNAs per vesicle is almost halved, and the number of receptors on each vesicle can be reduced by up to 70 percent, making them much less sticky,” he said.

How does this affect your ability to fight off colds, flu and Covid-19? It halves your immune system’s ability to fight off respiratory infections, says Bleier.

As it turns out, the pandemic has given us what we need to help fend off the cold air and keep our immunity high, Blair said.

Wearing a face mask can protect you from cold air, which can lower your immunity, an expert says.

“Not only does a mask protect you from direct inhalation of the virus, but it’s like wearing a sweater over your nose,” he said.

Patel agrees: “The warmer the intranasal environment, the better this innate immune defense mechanism works. Maybe there’s another reason to wear a mask!”

In the future, Bleier expects to see the development of topical nasal medications based on this scientific discovery. These new drugs “basically fool the nose into thinking it just found a virus,” he said.

“With this exposure, all these extra bumblebees are flying around in your mucus to protect you,” he adds.

Source link