Influenza is a notifiable condition in Victoria, and data for this article is taken from this notification data.
What happened
The severe 2017 influenza season resulted in unprecedented demand for health services throughout Victoria.
Increased numbers of people presented to general practices and hospitals with influenza-like illnesses.
The very young and the very old were particularly affected. Most children hospitalised with influenza were aged under five years, and there was a record number of respiratory outbreaks due to influenza reported in aged care facilities.
There were 48,200 laboratory-confirmed cases of influenza notified to the department in 2017, which was nearly five times higher than the previous five-year average, as shown in Figure 1 (Department of Health and Human Services 2018a).
Figure1: Notifications of laboratory-confirmed influenza, Victoria 2009–2017
Source: Department of Health and Human Services
Notifications began to rise in mid-July, peaked in early September, and did not drop down to usual inter-seasonal levels until late November.
Laboratory testing indicated the early peak was due to influenza type A (Figure 2), with the later, slightly lower peak due to influenza type B.
Figure 2: Notifications of laboratory-confirmed influenza by influenza type and week, Victoria, 2017
Source: Department of Health and Human Services
These types affected different age groups, with most type A from those under five years of age and those aged 65 years and older. Type B was most common in those aged five to nine years old (Figure 3).
Figure 3: Notifications of laboratory-confirmed influenza by influenza type and age group, Victoria, 2017
Source: Department of Health and Human Services
Hospitalisations and deaths
Between May and October 2017, the number of hospitalisations due to influenza was four times higher than the average for the previous five years (Department of Health and Human Services 2018b).
While there were more people admitted to intensive care units (ICUs) with influenza, ICU admissions for influenza as a percentage of all hospital admissions was 6.4 per cent, which was lower than the average for 2012–2016 of 9.3 per cent.
There were increased deaths in hospitalised influenza cases reported in 2017 (229 deaths) compared with an average of 53 deaths in each year from 2012–16.
These deaths in 2017 were mainly in elderly patients, which is consistent with years when this strain of influenza predominates.
Why did it happen
Findings from the World Health Organization Collaborating Centre for Reference and Research on Influenza indicated unusually poor effectiveness of the influenza vaccine used in 2017.
In particular, the vaccine had low effectiveness against the predominant influenza Type A strain, which was the main strain circulating throughout Australia in 2017 (Department of Health 2017).
This strain contained within the vaccine was replaced for the 2018 southern hemisphere influenza season.
Responding to the outbreak
The National Immunisation Program (NIP) includes free vaccination for groups known to be vulnerable to severe influenza infection.
This includes:
- people with underlying medical conditions
- Aboriginal and Torres Strait Islander peoples
- those aged 65 years and older
- pregnant women (Department of Health 2018).
Following the severe 2017 influenza season, several additional targeted vaccination programs were introduced.
From May 2018, Australian Government-subsidised providers of residential aged care were required to offer free influenza vaccination to all staff and volunteers.
Two new vaccines were added to the National Immunisation Program for people aged 65 years and older.
To help provide further community protection, the Victorian government implemented a special vaccine program in 2018 for children aged from six months up to five years.
The prolonged, high peak of influenza infections throughout the community in 2017 placed pressure on all areas of the Victorian health system.
Data collection from influenza surveillance systems has been enhanced to ensure early warning and appropriate resource allocation for future influenza seasons.
Find out more
Find out more about influenza.
References
Department of Health 2017, 2017 Influenza Season in Australia: a summary from the National Influenza Surveillance Committee, Commonwealth Government, Canberra.
Department of Health 2018, National immunisation program schedule, Commonwealth Government, Canberra.
Department of Health and Human Services 2018a, Notifications of influenza to Department of Health and Human Services, State Government of Victoria, Melbourne.
Department of Health and Human Services 2018b, Victorian admitted episodes dataset for influenza. State Government of Victoria, Melbourne.
Reviewed 11 March 2023