Why do people get sick with viruses in the winter?

Respiratory illnesses such as COVID 19 and influenza see a spike during the colder periods. This is not exclusively because people tend to stay indoors more during this time, according to Dr. Matthew Binnicker, who heads the Clinical Microbiology Molecular Lab and co-leads the Clinical Virology Lab at Mayo Clinic. Dr. Binnicker elaborates on the other elements that contribute to the rampant spread of viruses in winter.

He finds it intriguing to observe how respiratory viruses like COVID 19 and influenza display a regular rise in the infection rate amid the colder months in the Northern Hemisphere, typically from November to the end of February. "The popular assumption is that it occurs mainly due to more people staying indoors, which admittedly plays a part," mentions Dr. Binnicker.

However, another crucial aspect is humidity. Dr. Binnicker explains, "Higher humidity levels are observed during warmer months. When we talk, cough, or sneeze, the larger volumes of moisture present make any released droplets from our cough, sneezes, or speech bigger. These larger droplets descend to the ground or floor more rapidly."

On the contrary, drier conditions of the air in winter enable the possibility of smaller droplets containing a virus to remain in the atmosphere for more extended periods and spread farther. An individual's immunity is also compromised during the winter, as the cilia - tiny hair-like structures in the upper respiratory tract responsible for removing foreign bodies from our nostrils - operate less effectively in cooler temperatures and lower humidity.

Dr. Binnicker concludes, "This allows a virus to stay in our upper respiratory tract for an extended duration.” He suggests that besides adopting measures like vaccination and maintaining hand hygiene, employing humidifiers might aid in restricting the transmission of these viruses.