10 Influenza

Key information

Mode of transmission Spread by droplets generated by sneezing and coughing, by direct or indirect contact, or by the aerosol route.
Incubation period Usually 1–3 days (range 1–7 days).
Period of communicability From 1–2 days before symptoms start until about day 5 of illness; may be longer in young children and if immune compromised.
Disease burden Influenza epidemics occur each year. The highest burden of disease is in the very young, the elderly, pregnant women, those with co-morbid conditions, people from low income groups, and in Māori and Pacific ethnic groups.
Funded vaccines Trivalent inactivated split virion vaccines (Influvac; Fluarix).
Funded vaccine indications Recommended and funded for:
  • those aged 65 years and older
  • pregnant women
  • those aged under 65 years with high-risk conditions
  • ​children aged under 5 years who have been hospitalised for respiratory illness or have a history of significant respiratory illness.
Vaccine efficacy/effectiveness Depends on the match of the strains in the vaccine with circulating strains, the age of the individual and whether they have any underlying medical conditions.
Precautions Individuals who have had a confirmed anaphylactic reaction to egg protein may still be able to receive influenza vaccine, but should do so under specialist supervision.

There may be an increased risk of fever and febrile convulsions with concomitant PCV13 and influenza vaccine in children aged 6–59 months.
Adverse events Children aged under 5 years are more likely than older children or adults to have a febrile reaction to influenza vaccine.