Types of Influenza

Influenza is described by virus type, subtype and the way it occurs.

Virus types

• Influenza A: the most variable type, causing seasonal flu and pandemics. It is classed by two surface proteins, hemagglutinin (H) and neuraminidase (N), such as H1N1 and H3N2.
• Influenza B: has two main lineages (Victoria and Yamagata). It causes seasonal outbreaks, with more illness in children.
• Influenza C: causes mild respiratory illness.
• Influenza D: mainly affects cattle.

By pattern of occurrence

• Seasonal influenza: yearly outbreaks from circulating A and B strains
• Pandemic influenza: a new strain spreads worldwide because most people have little immunity
• Zoonotic influenza: infection from animals, such as avian influenza, which is rare in people but can be serious

By severity

• Uncomplicated influenza: fever, cough and aches that recover at home
• Complicated influenza: pneumonia, worsening of heart or lung conditions, or other complications

Related infections

Common cold, COVID-19 and other respiratory viruses can look similar. A test can help when the diagnosis matters.

Ayurvedic view

Traditional texts describe different jwara by dosha. These do not match modern virus types.

Key point

Seasonal flu vaccines are updated yearly to cover the most likely circulating A and B strains.

Before your appointment

Note when symptoms began, your highest temperature, and any cough, breathing trouble or vomiting. List your medicines, long-term conditions, pregnancy, allergies and recent vaccines, including this year's flu vaccine. Mention contact with anyone who is ill. Ask about testing, antivirals, when to return to work or school and the warning signs that mean you should call 112 or 102.