Influenza (flu) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness. The virus is transmitted easily from person to person via droplets. Influenza tends to spread rapidly in seasonal epidemics. Infection usually lasts for about a week, and is characterized by sudden onset of high fever, aching muscles, headache and severe malaise, non-productive cough and sore throat. Serious outcomes of influenza infection can result in hospitalization or death. Young children, pregnant women, older people and persons with certain health conditions are at a higher risk of getting influenza related complications.

Influenza viruses are constantly changing, and can infect both humans and animals (birds, pigs, horses). There are several types (namely A, B and C) and subtypes of the Influenza virus. In India, both seasonal influenza and avian influenza (in wild birds, poultry) have been widely reported.

Vaccination is recommended each year for protection against seasonal influenza. Antiviral drugs for influenza given early (within 48 hours of symptom onset) may reduce severe complications and deaths.