Influenza
Influenza (flu) is a respiratory infection caused mainly by influenza A and B viruses. It often starts suddenly and can feel much more intense than a common cold. Most people recover, but pneumonia and worsening of existing illnesses can occur. Young children, older adults, pregnant people and people with certain medical conditions face greater risk of complications.
Prevention: Mixed
Symptoms
- Sudden fever or chills, although fever is not always present
- Cough, sore throat and a runny nose
- Headache, muscle aches and marked tiredness
- Children may also have vomiting or diarrhea
Transmission
- Respiratory droplets and airborne particles from an infected person
- Touching contaminated surfaces and then the face
- Spread can occur before symptoms or without obvious illness
Prevention
Seasonal vaccination reduces risk and complications; follow local recommendations. Wash hands, reduce close contact while ill and take appropriate respiratory precautions. Flu seasons differ between hemispheres, and flu can circulate year-round in tropical regions.
Diagnosis and care
People at higher risk or with worsening illness should seek care promptly. Antiviral treatment can help, especially when started early. Breathing difficulty needs urgent assessment.
Source
- Influenza
Based on CDC information
Source language: English
Source reviewed: April 23, 2025
Source accessed: May 17, 2026
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