Effectiveness of influenza vaccine in reducing influenza-associated hospitalizations and deaths among the elderly population; Lazio region, Italy, season 2016-2017

ABSTRACT

Background

This study aimed to estimate influenza vaccine effectiveness (VE) in preventing influenza-related deaths and hospitalizations in the elderly population.

Methods

We retrospectively analyzed the cohort of 1,251,218 elderly aged ≥65 years who were residing in the Lazio region in 2016–2017. We estimated influenza VE using the Cox proportional hazards model, adjusting for demographic characteristics, preexisting health-risk conditions, and prior vaccinations.

Results

Estimated VE was 14% (95% confidence interval (CI): 11 to 17); 26% (95%CI: 19 to 33) in preventing influenza-related deaths and 13% (95%CI: 10 to 16) in preventing influenza-related hospitalizations. Seasonal VE was higher in the elderly vaccinated in prior seasons (VE = 20%, 95%CI: 17 to 23). We found no significant differences in effectiveness by vaccine type, although the MF59-adjuvanted vaccine appeared more effective than other vaccines in individuals aged ≥75 years, particularly in those aged ≥90 years (VE = 18%, 95%CI: 9 to 26).

Conclusions

Although VE was low, vaccination still provided benefits in preventing influenza-related hospitalizations and deaths in the elderly, particularly among those vaccinated in prior seasons. Efforts should therefore be made to improve vaccine uptake and the utilization of vaccines with greater effectiveness in the oldest elderly (e.g. high-dose and adjuvanted cell-based vaccines).

KEYWORDS:

• Elderly population
• deaths
• hospital admissions
• influenza
• vaccine effectiveness

Acknowledgments

We would like to thank Dr Paola Michelozzi and Dr Daniela Porta (Department of Epidemiology, Lazio Regional Health Service) for having provided data from the deaths registry.

Author Contributions

M Fabiani, P Pezzotti, and F Chini conceived the study. All authors provided substantial contribution to the study design. E Volpe, M Faraone, A Bella, and F Chini retrieved and managed the data. M Fabiani, P Pezzotti and F Chini performed the statistical analysis. M Fabiani drafted the manuscript. All authors critically revised the manuscript and approved its final version.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer Disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Data availability

The data that support the findings of this study are not publicly available due to legal restrictions. The data are available from the corresponding author, M Fabiani, upon reasonable request and with the permission of the Lazio region authorities.

Additional information

Funding

This paper was not funded.