Does the winter equal flu season?

Last updated on November 22, 2023 First published on November 20, 2023

Colds and flu are often associated with the cold season. It almost feels as if viruses only exist in winter. But is that really the case?

“In fact, four out of five viral respiratory infections occur in the winter months,” confirms Walter Zingg, Head Physician at the Department for Infectious Diseases and Hospital Hygiene at the USZ. And this despite the fact that the pathogens are on the move all year round. “This is mainly due to the fact that we are spending more time indoors.” In most cases, the immune system can intervene quickly and fight pathogens very effectively. “However, an immune response to respiratory viruses does not last forever, and new virus strains circulate every season, challenging the immune system anew,” explains Walter Zingg. This can also give otherwise healthy people the impression that they are almost exclusively ill in winter. However, this trains the immune system and we go into spring and summer with a strengthened immune system.

Easy game for viruses in winter

In addition to the immune response, there are other factors that favor infection during the cold season. “They are based on a combination of different circumstances,” says Huldrych Günthard, Deputy Director of the Department for Infectious Diseases and Hospital Hygiene. Low humidity plays a role: viruses survive longer in dry air and spread better.

“In addition, the mucous membranes in the airways are also drier, which makes them more susceptible to infection. The formation of nasal secretions, for example, is the body’s first defense reaction.” Contact with other people is also closer in the winter months as we spend more time indoors. “Colds are often accompanied by coughing and sneezing. This means that the pathogens can easily spread to people in the vicinity,” explains Günthard.

Viral or bacterial infection?

It’s not just viruses that circulate in the cold season, bacteria also cause infections. The distinction is important because the treatment is fundamentally different: Vaccinations are possible against many viruses, while bacterial infections are treated with antibiotics. Laboratory analysis, for example of a throat swab or sputum, is used to determine the pathogen so that antibiotic therapy can be targeted. Good hand hygiene and social distancing are equally important for viral and bacterial infections.

Walter Zingg, PD Dr. med.

Senior Attending Physician, Department of Infectious Diseases and Hospital Epidemiology

Tel. +41 44 255 33 22
Specialties: Infectiology, Hospital hygiene, Pediatrics

Huldrych Günthard, Prof. Dr. med.

Senior Attending Physician, Department of Infectious Diseases and Hospital Epidemiology

Tel. +41 44 255 33 22
Specialties: HIV infection, antiretroviral therapy, Opportunistic infections in immunocompromised patients, Viral infections