Young healthy adults generally recover well. The consequences may be more serious for infants, children born prematurely up to the age of two, people aged 65 or over, pregnant women and people suffering from certain chronic diseases or immune deficiency.

Flu sometimes causes complications, whether from the influenza virus itself or from a bacterial secondary infection, e.g. middle ear infection, pneumonia or inflammation of the heart muscle.

On average, seasonal flu is responsible for around 111,000 to 331,000 doctor's consultations, several thousand hospitalisations and several hundred deaths every year in Switzerland. Ninety per cent of the deaths from flu affect people aged 65 or over.

Co-infection "flurona"
When coronaviruses and influenza viruses circulate concurrently, especially in winter, co-infections with influenza and covid-19 can occur.

This double infection with both viruses, which occurs at the same time or shortly after one another, is colloquially and in the media sometimes called "flurona". This is neither a new virus nor a new disease.

As an approximate rule, the symptoms and severity of such co-infections are a combination of the individual infections. In particular, for persons who have an increased risk of influenza complications or an increased risk of a severe covid-19 course, a co-infection with influenza and SARS-CoV2 carries additional risks. This is especially true for persons who have no or only insufficient immunity - due to previous infection or thanks to vaccination.

The best protection is a vaccination against both pathogens. Currently (as of 28 January 2022), persons with an increased risk of influenza complications and their close contacts can still be vaccinated against seasonal influenza.