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The influenza virus is highly infectious. This combined with a short incubation period (likely 1–3 days, maximum 7 days) and a period of viral shedding (when a person can infect others – 1 day before symptoms and up to 7 days after onset of illness in adults and up to 21 days in young children),12 accounts for the rapid spread of the influenza virus.
The primary mode of transmission is by large respiratory droplets, which can be propelled up to 1 metre from an infected person who is coughing or sneezing, onto the mouth, nose or eyes (mucous membranes) of another person.
Spread is also by direct or indirect (fomite) contact, when a person touches respiratory droplets that are on either another person or an object and then touches their own mouth or nose.
Airborne (small particles) transmission can occur in the general practice setting by particles being dispersed during the use of nebulisers, oxygen administration and intubation. These procedures should not be undertaken without appropriate personal protective equipment (PPE).
Evidence shows that physical barriers, especially hand hygiene, wearing a mask, and using social distancing or isolation of potentially infected people, are effective in preventing the spread of respiratory virus infections.13
Animal studies regarding the transmission of influenza viruses have pointed to a number of environmental factors, including relative humidity and temperature, that may influence transmission.14