Read condition-specific symptoms and clinical context for Human influenza viruses. Respiratory viruses with illness ranging from mild to severe.
This human-focused clinical group covers influenza illness rather than a single viral species. Symptoms often start suddenly. Influenza can cause mild or severe disease, and some people develop complications such as pneumonia.
A person may have some of these symptoms. Not everyone with flu has a fever.
Possible symptoms: Fever or chills; Cough; Sore throat; Runny or blocked nose; Body aches or headache; Fatigue.
Seek urgent medical care for warning signs such as breathing difficulty or persistent chest pressure. Symptoms alone cannot reliably distinguish flu from COVID-19.
Source check: 2026-09-19. Educational content; independent scientific review remains pending.