Last year, influenza vaccination campaigns targeted avoidance of the ‘twindemic’ of concomitant COVID-19 and influenza. In 2021, a strong vaccination effort will help protect against a major winter outbreak of these diseases.
- In 2020, influenza case numbers between April and September were less than 5% of the previous five-year average.
- Although the extent of the upcoming influenza season is unknown, early data suggest a significant outbreak is not likely. However, if there is reduced immunity due to the absent 2020 season and the virus arrives, influenza activity may be high.
- With few COVID-19 cases in Australia, there will not be viral competition to stop the spread of influenza here.
- For older people, adjuvanted influenza vaccines have been shown to overcome the usual poor immune response due to immunosenescence and chronic, sterile, low-grade inflammation (‘inflammaging’).
- Continuing to improve uptake of influenza vaccine in children will be important in 2021.
- Quadrivalent cell-based influenza vaccines are available for the first time this year.
- SARS-CoV-2 will continue to be a risk to Australia through overseas arrivals.
- A strong vaccination effort by primary care physicians and other healthcare providers will be key this winter.
Influenza in recent years
In 2019, Australia saw its most intense influenza season since accurate collation of data began, with over 300,000 laboratory confirmed notifications to the National Notifiable Disease Surveillance System.1 The notifications were mainly for the H3N2 strain of influenza A, which causes disease predominantly in older people. The outbreak occurred despite a record distribution at that time of 14.5 million influenza vaccines in Australia. It was associated with an estimated 3000 deaths.1
Amid the high volume of disease in 2019 there were some exciting data about the impact of using an adjuvanted vaccine in the elderly. The aim of influenza vaccination is not preventing influenza disease but maintaining functional capacity, which in elderly people means avoiding the prolonged bed rest of hospitalisation. Queensland surveillance data show that although the amount of illness in people aged over 65 years was comparable in 2017 and 2019 – which were both intense years for influenza – the hospitalisation rate in 2019 was 60% lower for this age group.2,3 This was the first year only adjuvanted vaccine and no other vaccine was used in older people.
Published data from the WHO Collaborating Centre for Reference and Research on Influenza for vaccine effectiveness in the southern winter of 2019 explains this.4 Vaccine effectiveness against the H3N2 strain was actually highest in the over-65 years age group – a finding never seen previously, when using unadjuvanted vaccines in older people. The adjuvanted vaccine overcame the usual poor immune response that is caused by immunosenescence and the chronic, sterile, low-grade inflammation (‘inflammaging’) that is present in older people.