Influenza continues to cause a substantial burden on the community. Widening recommendations, a focus on vaccinating children, improved access to funded vaccination and new enhanced vaccines for older adults are all aimed at improving control of influenza.
- Influenza is increasingly recognised as being responsible for a large burden of disease not only in older people and people with medical conditions that increase the risk of severe influenza, but also in healthy young children, pregnant women and Indigenous Australians.
- Vaccination provides good protection and is recommended for all people from 6 months of age.
- Age-appropriate vaccines should be used in children; enhanced vaccines, which induce a stronger immune response, are preferentially recommended for people aged 65 years and over.
- Free vaccination under the National Immunisation Program is available for older adults, people with certain comorbid conditions, pregnant women and all Aboriginal and Torres Strait Islander people. State-funded programs provide free vaccine for children aged from 6 months to under 5 years of age.
Influenza is a common viral respiratory infection that causes a large burden of disease globally, through annual (typically winter season) epidemics. It is the most common vaccine-preventable disease in Australia.1 Although it is of mild-to-moderate severity in most people, severe disease can occur in previously healthy people of any age, but especially older people and those with comorbidities. Worldwide, influenza is estimated to cause three to five million cases of severe illness and about 290,000 to 650,000 respiratory deaths each year.2
Influenza epidemiology in Australia
Influenza has the greatest impact on the community at the extremes of age – the young and older people – as well as among those with medical comorbidities. Documented hospitalisation and mortality rates underestimate the true disease burden of influenza, in part owing to incomplete recognition of disease, undertesting and late complications of infection (such as bacterial pneumonia or myocardial infarction).
Because of immunosenescence and an increased prevalence of comorbid conditions associated with severe influenza, older people have increased mortality and morbidity from influenza (Box 1).3,4 Less well known is the high burden of disease among other groups, such as children younger than 5 years who are often otherwise healthy. Young children have similar or higher hospitalisation rates due to influenza than older adults (108 to 187 per 100,000 in those aged under 2 years compared with 48 per 100,000 in those aged 75 years and over).5 Infection attack rates in the unvaccinated community are highest among children, estimated at 15 to 22.5% annually, and infected children are significant in the spread of influenza to the rest of the community.6-9 The incidence of influenza among babies under 6 months, who are too young to be vaccinated, is substantial. 5 They benefit from maternal vaccination during pregnancy, which results in transplacental transfer of high levels of influenza-specific antibody.10