Influenza: Vaccine Preventable Diseases Surveillance Standards

Overview

Influenza viruses are orthomyxoviruses that cause acute respiratory illness, ranging from mild febrile illness accompanied by body aches, cough and sore throat to severe pneumonia, which can be complicated by bacterial superinfection. Influenza viruses that infect humans are transmitted person to person, mostly by droplets and aerosols from the respiratory secretions of infected people, and occasionally from fomites or animals.

Influenza viruses cause seasonal influenza epidemics, mostly in the winter months in temperate climates and with less distinct seasonality in the tropics, with annual attack rates of 5–10% in adults and 20–30% in children (1). Groups at higher risk of severe illness include young children, pregnant woman, the elderly and those with underlying medical conditions. The incubation period is one to four days. In general, the disease burden of influenza in lower- and middle-income countries has been underestimated.