Medical Encyclopaedia › Flu (short definition)
In brief: True flu (influenza) is an acute respiratory infection caused by influenza viruses. It usually begins suddenly with a high fever and a strong feeling of illness and can be dangerous, particularly for older and chronically ill people.
Symptoms
Typical features are a sudden onset with fever above 38.5 °C, chills, pronounced muscle aches and headache, a dry cough and great exhaustion. Recovery can take one to two weeks or longer.
Transmission and complications
Influenza viruses are transmitted mainly via droplets when coughing and sneezing. Possible complications are pneumonia, myocarditis and worsening of existing heart or lung diseases. People aged 60 and over, pregnant women, the chronically ill and residents of care homes are particularly at risk.
Flu vaccination
Annual vaccination in autumn is the most effective prevention. In Germany, the Standing Committee on Vaccination (STIKO) recommends it for, among others, people aged 60 and over, pregnant women, the chronically ill and medical and nursing staff. As the viruses are constantly changing, the vaccine is adapted every year.
Treatment
Bed rest, sufficient fluids and fever-reducing painkillers relieve the symptoms. For high-risk patients, antiviral medicines can be useful; they should be taken within 48 hours of symptom onset if possible. Antibiotics only help with additional bacterial infections. Shortness of breath, chest pain or confusion require immediate medical help.
Related terms in the encyclopaedia
Common cold, Vaccination, Pneumonia, Fever, Myocarditis
Sources
- Robert Koch-Institut (RKI): RKI-Ratgeber Influenza
- Ständige Impfkommission (STIKO): Impfempfehlungen, Epidemiologisches Bulletin
- IQWiG: gesundheitsinformation.de – Gesundheitsinformationen des Instituts für Qualität und Wirtschaftlichkeit im Gesundheitswesen
Note: This article is for general information and does not replace advice, diagnosis or treatment from a doctor or pharmacist. Last updated: October 2026.