Causes of Influenza

Influenza is caused by influenza viruses. The illness spreads easily from person to person.

The viruses

• Influenza A: causes seasonal outbreaks and occasional pandemics. It is named by subtypes such as H1N1 and H3N2.
• Influenza B: causes seasonal outbreaks, usually milder than A, but can still be serious.
• Influenza C: causes mild illness.
• Influenza D: mainly affects cattle and is not known to cause illness in people.

Why it comes every year

The viruses change slightly over time (antigenic drift), so previous infection or vaccination may not fully protect against new strains. This is why the vaccine is updated yearly.

How it spreads

• Tiny droplets from coughs, sneezes and speech reaching others nearby
• Contact with surfaces or hands carrying the virus, then touching the eyes, nose or mouth
• Crowded, closed spaces make spread easier.

What raises the chance of catching it

• Close contact with someone who has flu
• Not being vaccinated
• Crowded places such as schools, offices and public transport
• Weak immunity, chronic illness, pregnancy, very young or old age
• Poor sleep and high stress, which may reduce resistance

Animal influenza

Rarely, viruses from birds or pigs infect people, usually after close contact with animals. Seek medical advice if you become ill after such contact.

Ayurvedic view

Ayurveda links seasonal fevers to aggravated doshas with weak digestion and changing weather. This is a traditional framework and not a modern explanation.

Key point

Flu is caused by a virus, so antibiotics do not treat it.

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.