Secondary bacterial infections: Life-threatening influenzais often caused by secondary bacterial infections with staphy-lococci, pneumococci, and Haemophilus influenzae. Pneumonia may develop as a complication and may be fatal, particularly (a) in elderly persons above 60 years with underlying chronic disease, (b) in people with impaired resistance (chronic cardiore-spiratory disease, renal disease, etc.), and (c) in pregnant women.
Central nervous system complications: Guillain–Barre syn-drome characterized by encephalomyelitis and polyneuritis is a rare complication of influenza virus infection. This condition was documented in the United States in the year 1976, following extensive vaccination with inactivated H3N2 influenza virus.
Other complications: Reye’s syndrome is a noted compli-cation of influenza B infection. The condition is seen most commonly in young children and is associated with degenera-tive changes in the brain, liver, and kidney.