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Meta-Analysis
. 2021 Mar;15(2):293-314.
doi: 10.1111/irv.12814. Epub 2020 Sep 30.

Epidemiology and burden of illness of seasonal influenza among the elderly in Japan: A systematic literature review and vaccine effectiveness meta-analysis

Kiyosu Taniguchi  1 , Shunya Ikeda  2 , Yuriko Hagiwara  3   4 , Daisuke Tsuzuki  3 , Marwa Klai  5 , Yoko Sakai  6 , Bruce Crawford  6 , Joshua Nealon  5
Affiliations
Meta-Analysis

Epidemiology and burden of illness of seasonal influenza among the elderly in Japan: A systematic literature review and vaccine effectiveness meta-analysis

Kiyosu Taniguchi et al. Influenza Other Respir Viruses. 2021 Mar.

Abstract

Background: Elderly populations are particularly vulnerable to influenza and often require extensive clinical support. In Japan, nationwide passive surveillance monitors seasonal influenza but does not capture the full disease burden. We synthesized existing evidence on the epidemiology, vaccine effectiveness (VE), and economic burden of seasonal influenza in the elderly population.

Methods: PubMed, EMBASE, and ICHUSHI were searched for articles on seasonal influenza in Japan, published between 1997 and 2018, in English or Japanese. Grey literature was also assessed. A random-effects meta-analysis characterized VE of influenza vaccines among studies reporting this information.

Results: Of 1,147 identified articles, 143 met inclusion criteria. Reported incidence rates varied considerably depending on study design, season, study setting and, most importantly, case definition. In nursing homes, the maximum reported attack rate was 55.2% and in the 16 articles reporting mortality rates, case fatality rates varied from 0.009% to 14.3%. Most hospitalizations were in people aged >60; healthcare costs were partially mitigated by vaccine administration. Meta-analysis estimated overall VE of 19.1% (95% CI: 2.3% - 33.0%) with a high proportion of heterogeneity (I2 : 89.1%). There was a trend of lower VE in older people (40.1% [-57.3-77.2] in the <65 group; 12.9% [-8.0-29.8] in those 65; P = .21).

Conclusions: Despite differences between studies that make comparisons challenging, the influenza burden in elderly Japanese is significant. While vaccines are effective, current vaccination programs offer suboptimal protection. Health economic data and cost-effectiveness analyses were limited and represent areas for policy-relevant future research.

Keywords: Japan; economic burden; elderly; epidemiology; meta-analysis; seasonal influenza; systematic literature review; vaccine effectiveness.

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Conflict of interest statement

Joshua Nealon, Yuriko Hagiwara are employed by Sanofi Pasteur, a company which produces influenza vaccines. Daisuke Tsuzuki and Marwa Klai were working at Sanofi at the time of performing the study.

Figures

Figure 1
Figure 1
Article Selection Procedure – PRISMA flow chart. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta‐Analyses
Figure 2
Figure 2
Age distribution of influenza hospitalization in Japan. Data reproduced from National Institute of Infectious Diseases. 23 CI, confidence interval; ES, effect size; LCI, Laboratory‐confirmed influenza; RTI, respiratory tract infection
Figure 3
Figure 3
Forest plot of vaccine effectiveness estimates and the overall pooled estimate from a random‐effects model without adjustments (diamond). Boxes represent estimates weighted by the inverse of their variance, lines 95% CIs
Figure 4
Figure 4
A‐D, Forest plot of vaccine effectiveness estimates stratified by (A) age group; (B) study setting; (C) study design and (D) circulating subtype. Diamonds represent pooled estimates per subgroup from a random‐effects model without adjustments. Boxes represent estimates weighted by the inverse of their variance, lines 95% CIs
See this image and copyright information in PMC

References

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