9 January 2020
An Australian study has confirmed flu vaccination effectively reduces mortality from the disease – positive news after a horror flu season.
Epidemiologist and research assistant at the Murdoch Children’s Research Institute, Monica Nation, and her research team, were keen to fill an evidence gap in what we know about vaccination and influenza.
‘The simplest way to prevent influenza infection and hospitalisation is vaccination, but there is limited evidence about how effective influenza vaccination is against influenza-related mortality,’ she explained to newsGP.
Ms Nation and her research team worked on this problem using a case-control model and large-scale patient data collected nationally across Australia, mostly among the target group of the National Immunisation Program (NIP), who comprised 84% of the patients included in the study.
‘We used data collected over eight influenza seasons from a national hospital-based influenza surveillance system which included 17 Australian hospitals and over 15,000 patients admitted with laboratory-confirmed influenza,’ Ms Nation said.
‘We found that influenza vaccine reduced the risk of influenza-related mortality by 31%, including in the National Immunisation Program target group.’
The resulting study, which was published in Clinical infectious diseases earlier this week, concluded that its ‘finding reinforces the utility of the Australian vaccination program in protecting those most at risk of influenza-related deaths’.
Professor Allen Cheng, infectious diseases physician and study co-author, explained to newsGP that extra care was taken in this study to isolate the effects of vaccination as much as possible from other factors.
‘Observational studies such as these have been plagued by “confounding” – people who tend to get vaccinated also tend to do other things that make them healthier, which is known as the “healthy user” effect,’ he said.
‘Conversely, we deliberately target influenza vaccination at people with chronic illnesses who have a higher risk of death – this is known as “confounding by indication”.
‘We were able to carefully control for these factors using a statistical technique called propensity scoring. We were also able to check if this worked by looking at non-influenza deaths, with the rationale that influenza vaccine shouldn’t protect against non-influenza deaths.’
Professor Cheng observed that current vaccinations only provide moderate protection against infection, hospitalisation and mortality, so there is a need for a more effective vaccine to reduce the burden of the disease.
‘On the other hand, we are confident there is some protective effect, so getting vaccinated is better than not being vaccinated,’ he said.
The results also provide additional support for the continued implementation of the NIP, and further, its greater expansion in future – which would perhaps be welcomed by many after what was often referred to as a ‘horror’ flu season in 2019.
‘This study reinforces the importance of the national influenza immunisation program, which immunises those most at risk of severe influenza outcomes such as death,’ Ms Nation said. ‘It also suggests that we could reduce deaths from influenza further if vaccination coverage were higher.
‘This study was performed before the “enhanced” or adjuvanted and high dose vaccines became available, so protection may be better with these vaccines.’
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