The determinants of influenza vaccination effectiveness in people aged 65 years and older : a systematic review

Abstract

Background Influenza vaccination effectiveness is generally lower in people aged 65 years and above compared with healthy adults below the age of 65. While this is generally attributed to weaker immune response in the elder population as a result of immunosenescence, the reasons for this phenomenon are not well characterised. The aim of this systematic review is to identify, investigate and summarise documented determinants of seasonal vaccine effectiveness in the elderly population.

Methods A literature search was conducted on bibliographic databases PubMed and EMBASE to identify relevant articles that investigate the determinants of influenza vaccine effectiveness in the elder population up to July 4, 2015.

Findings Out of 37 relevant studies that were identified through the search process, eight studies that assess potential determinants of influenza vaccine effectiveness in the elder population were identified. The determinants that were described include vaccine type and route of administration, time elapsed after vaccination, frailty, and pneumococcal vaccination. While this list of determinants is not exhaustive, they were determinants that were assessed using endpoints that are linked to confirmed diagnosis of influenza among studies identified in this review.

Conclusions Besides antigenic match, documented determinants of influenza vaccine effectiveness in the elder population can be broadly categorized into vaccine factors, host factors, and vaccination policies and strategies. Nevertheless, published studies that assess the impact of these determinants are relatively scarce and have lower internal validity as they are observational in nature. Due to the heterogeneity of endpoints used to assess vaccine effectiveness, these studies are often not directly comparable. There is a need for more well-designed observational studies to identify and investigate the determinants of vaccine effectiveness in elder individuals, as they are at a higher risk of developing serious complications of influenza. The identification of these determinants will facilitate efforts to improve influenza vaccination in elder individuals.