  The Case for Influenza Vaccination
Influenza infection is associated with significant morbidity and mortality
in the elderly and certain high-risk groups.13 Influenza infection can
cause a variety of diseases, ranging from mild asymptomatic infection to
serious complications such as pneumonia, exacerbations of chronic
respiratory disease, myocarditis and pericarditis, encephalitis,
haematological disorders and death from primary or secondary bacterial
pneumonia.1,2,13 The development and severity of complications is
influenced by a person's age, pre-existing medical conditions, virulence
of the virus strain and past exposure to related influenza virus.1
Influenza vaccination is the most important way of preventing and
attenuating influenza infection and preventing mortality in people at
risk of complications.1 Vaccination against influenza has been shown to
reduce morbidity and mortality from respiratory and circulatory disease
during annual influenza epidemics in those aged over 65 years and those
at high risk of infection.1
Types of influenza vaccines available in Australia
Influenza viruses are classified based on serotype (A, B or C) as well as
geographical location of first isolation, strain serial number and year
of isolation. Influenza A and B are associated with human disease, and
are the targets of influenza vaccines. All vaccines available in
Australia are either split virion or subunit vaccines, usually
containing three strains of the virus - 2 current A subtypes and 1
influenza B - that represent recently circulating viruses. Both split
virion and subunit vaccines are prepared from purified inactivated
influenza virus and cultivated from embryonated hens' eggs. They are
considered similar in terms of efficacy and safety, and both are better
tolerated than whole virus vaccines.1
The overall effectiveness of influenza vaccines depends on the age and
immunocompetence of the recipient, as well as the similarity between
virus in the vaccine and circulating virus in the community.1 Most
vaccines offer protection for up to 12 months, with a low level of
protection for a further 12 months against similar strains. Annual
vaccination against current strains is therefore recommended.1
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