Influenza viruses are spread person to person by droplet infection and small particle aerosol.
Droplets generally travel only a smaller distance (< 2 metres) while aerosol may go further. The virus replicates in the cells of the upper respiratory tract and going on to affect adjacent cells. Local mucosal immunity develops and there is a rise in serum antibodies.
Individuals are most contagious in the first 3 days after the onset of symptoms but probably shed the virus for about 5 days. A person can be infectious the day before they develop symptoms. Those who are immune-suppressed or who have chronic disease shed the virus for longer.
The virus can remain viable on surfaces for hours in dried secretions before transfer to the respiratory tract. The incubation period (time between exposure and symptom onset) is 1 to 2 days.
Many Australians die from the complications of influenza every year. Most of these are over 65 years or under 5 years of age. Many have contributing health factors which make the illness worse.
On average there are approximately 13,500 hospitalisations and 300,000 GP consultations every year in Australia due to influenza virus.
Influenza A and B are common respiratory illnesses, particularly in the winter months. These viruses undergo frequent changes in their surface structure and can be responsible for major outbreaks, including pandemics.
The global situation is constantly monitored by the WHO and each year recommendations are provided for the constituents of an influenza vaccine for the winters of the Northern and Southern Hemispheres. Technical information on the vaccine is published twice yearly, in February and September. If there is a good match between the vaccine and the circulating strains, then there should be around 70-90% protection against clinical disease. In the elderly, the vaccine has been shown to reduce hospitalisations by 25-40% and deaths by up to 75%.
In Australia, influenza vaccine is provided free to certain groups under the National Immunisation Program.
These groups include:
- Children aged 6 months to less than 5 years.
- All aboriginal and Torres Strait Islander people aged 6 months and over.
- People aged 6 months and over with certain medical conditions that increase their risk of severe disease.
- Pregnant women.
- People aged 65 years and over.
Vaccine uptake is still an issue in those at risk of serious disease. In those over 65 years, the national uptake is just 70%.
Those not eligible for a free government funded influenza vaccine can purchase and have administered the vaccine privately through their GP or local pharmacy for around $20-$30.
