Abstract
Influenza vaccination may limit the impact of influenza in the community. The aim of this study was to assess the effectiveness of influenza vaccination in preventing hospitalisation in individuals aged ≥ 65 years in Spain. A multicentre case–control study was conducted in 20 Spanish hospitals during 2013/14 and 2014/15. Patients aged ≥ 65 years who were hospitalised with laboratory-confirmed influenza were matched with controls according to sex, age and date of hospitalisation. Adjusted vaccine effectiveness (VE) was calculated by multivariate conditional logistic regression. A total of 728 cases and 1,826 matched controls were included in the study. Overall VE was 36% (95% confidence interval (CI): 22–47). VE was 51% (95% CI: 15–71) in patients without high-risk medical conditions and 30% (95% CI: 14–44) in patients with them. VE was 39% (95% CI: 20–53) in patients aged 65–79 years and 34% (95% CI: 11–51) in patients aged ≥ 80 years, and was greater against the influenza A(H1N1)pdm09 subtype than the A(H3N2) subtype. Influenza vaccination was effective in preventing hospitalisations of elderly individuals.
Highlights
Influenza is an acute illness caused by influenza viruses
Of the 433 cases from the 2013/14 season, 429 (99.1%) were infected with influenza A virus (59.8% were A(H1N1)pdm09, 30.5% were A(H3N2) and 8.8% were unsubtyped), two cases were infected with influenza B virus and two cases were missing data for type and subtype
The results of this study over two seasons, one with predominant circulation of influenza A (H1N1)pdm09 and one with A(H3N2) predominance, show overall vaccine effectiveness (VE) against hospitalisation in individuals aged ≥ 65 years was 36%
Summary
Influenza is an acute illness caused by influenza viruses. Large numbers of influenza infections occur in all age groups. Influenza is a self-limiting illness, but serious secondary complications appear in some of those infected with the influenza viruses. The illness may result in hospitalisation, overwhelming hospitals and causing excess influenza health-related deaths [1]. Annual epidemics are estimated to result in ca 3 to 5 million cases of severe illness and ca 250,000 to 500,000 deaths [2]. Individuals who are elderly, especially those with comorbidities, are at risk for influenza-related complications and frequently require hospitalisation. A recent French study estimated that 11% of all-cause deaths in elderly individuals during the influenza season were attributable to influenza [4]. Mortality is just the tip of the iceberg in terms of disease and the economic burden, and hospitalisation is an important outcome that should be considered [5]
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