Abstract
Influenza has many age‐dependent characteristics. A previous systematic review of randomized controlled trials showed that the detection rate of influenza B was higher in children than in non‐elderly adults. However, no comprehensive reviews have targeted the elderly, who carry the main burden of disease. We aimed to quantify the relative detection rates of virus types A and B among the elderly, to identify factors affecting these proportions, and to compare type distribution among seniors and younger age‐classes. A comprehensive literature search was conducted to identify multiseason studies reporting A and B virus type distributions in the elderly. A random‐effects meta‐analysis was planned to quantify the prevalence of type B among elderly subjects with laboratory‐confirmed influenza. Meta‐regression was then applied to explain the sources of heterogeneity. Across 27 estimates identified, the type B detection rate among seniors varied from 5% to 37%. Meta‐analysis was not feasible owing to high heterogeneity (I 2 = 98.5%). Meta‐regression analysis showed that study characteristics, such as number of seasons included, hemisphere, and setting, could have contributed to the heterogeneity observed. The final adjusted model showed that studies that included both outpatients and inpatients reported a significantly (P = .024) lower proportion than those involving outpatients only. The detection rate of type B among the elderly was generally lower than in children/adolescents, but not non‐elderly adults. Influenza virus type B has a relatively low detection rate in older adults, especially in settings covering both inpatients and outpatients. Public health implications are discussed.
Highlights
Like that of many other infectious diseases, the epidemiology of influenza displays several age-dependent features
We considered only laboratory-confirmed influenza, studies with clear virus type and age-class distributions, a sufficient period of time [to avoid short-period studies driven by a singletype] and number of viruses detected among the study population
We demonstrated that the type-specific detection rate (DR) among the elderly may depend on study characteristics, such as the type of surveillance system
Summary
Like that of many other infectious diseases, the epidemiology of influenza displays several age-dependent features. Owing to the lack of data on vaccine efficacy/effectiveness (VE) in the various age-classes, the relative advantage of the recently introduced quadrivalent influenza vaccine (QIV) (which contains both IVB lineages) over trivalent (TIV) formulations has usually been calculated mathematically[15,16,17] from a set of epidemiological parameters These have included, for example, the mean relative detection rate (DR) of IVB, the mean level of lineage mismatch between the IVB included in TIV and that in circulation, and a meta-analytically obtained level of cross-lineage protection provided by TIV. Given the variety of influenza vaccines available for immunization (such as trivalent and quadrivalent, adjuvanted and non-adjuvanted),[22] insights from this epidemiological review could be helpful in future pharmacoeconomic and health technology assessment (HTA) evaluations aimed at establishing an equitable vaccination policy
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