Why the cold plays key part in contracting flu and other viruses

The nasal immune response falters when temperatures drop, scientists have discovered.

Scientists have uncovered the biological reason why colds are more common in colder temperatures.

A study suggests the newly discovered immune response inside the nose is suppressed by colder temperatures, and the illnesses are not more common simply because people are stuck indoors.

Scientists say this finding offers the first biological evidence for why respiratory illnesses such as colds, flu and Covid are more likely to spike when the temperature drops.

The upper respiratory tract (nose, mouth and throat) is the primary way people get infected through either inhaling the bug or depositing it with their hands.

Researchers at Mass Eye and Ear hospital and Northeastern University in America have discovered a previously unidentified immune response inside the nose that fights off viruses responsible for upper respiratory infections. Further testing revealed this response becomes blocked in the cold.

Benjamin Bleier, senior author of the study, said: “Conventionally, it was thought that cold and flu season occurred in cooler months because people are stuck indoors more where airborne viruses could spread more easily.

“Our study, however, points to a biological root cause for the seasonal variation in upper respiratory viral infections we see each year, most recently demonstrated throughout the Covid-19 pandemic.”

A 2018 study led by Dr Bleier and Mansoor Amiji, distinguished professor of pharmaceutical sciences at Northeastern University, uncovered an innate immune response triggered when bacteria is inhaled through the nose.

It found that cells in the front of the nose detected the bacteria and then released billions of tiny fluid-filled sacs called extracellular vesicles into the mucus to surround and attack the bacteria.

For the new study, the researchers wanted to see if this immune response was also triggered by viruses inhaled through the nose, which are the source of some of the most common upper respiratory infections.

According to the study, the number of virus-fighting sacs released fell by nearly 42pc when temperatures were reduced significantly for test subjects.

The new study is published in The Journal of Allergy and Clinical Immunology

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