Table 1. Study characteristics of included studies.

Source	Objective	Type	Based on	Currency	Analytic horizon	Dis-counting	Influenza outcome	Impact	Uncertainty analysis	Funding source
Aballéa et al.40	Economic evaluation of lowering the age threshold in various countries for influenza vaccination from currently 60 or 65 y to all people aged 50 y and older	CUA	Model	Brazilian real	Not reported	Life expectancy in unadjusted life years and quality-adjusted life years (3% per annum)	ILI; minor complications; hospitalization for pneumonia and influenza, for other respiratory complications, and other complications; and deaths	QALY gained	One-way sensitivity/ threshold analysis and PSA	IVS International Task Force
Chicaiza-Becerra et al.41	Cost-effectiveness evaluation of implementing a vaccination program for health workers in contact with hospitalized oncological patients	CEA	Model	Colombian peso	Not reported	Not applicable	Days hospitalized for influenza-related complications	Cost-effectiveness ratio (additional days of hospitalization prevented)	One-way sensitivity analysis for different transmission probabilities	Not specifically mentioned
Dayan et al.24	To compare from the societal perspective the costs and benefits of a general influenza vaccination program in high-risk children with no vaccination	CEA	Model	US dollars	12 mo	Not applicable	Influenza outcomes including outpatient visits, otitis media and hospitalization	influenza episodes averted	One-way sensitivity/ threshold analysis and PSA	Not specifically mentioned
Gutiérrez et al.43	Estimation of costs and health outcomes achievable by vaccination of people aged 65 y and older	CEA	Model	Mexican peso	5 mo	Costs per life year saved by different discount rates (3% assumed as bases, estimates provided for 0%, 5%, 10%)	Pneumonia-and influenza-associated deaths and cases	Life years saved, costs per life year saved	PSA	National public health institute
Porras-Ramirez et al.42	Evaluating the economic value of influenza vaccination of infants aged below 2 y and elderly aged 65 y and above	CEA	Model	US dollars	1 y	3% discounting	Among below 2 y old: annual number of cases of ARI, medical visits, hospitalizations and deaths from ARI Among 65 y and above: annual number of deaths and hospitalizations due to cardiocirculatory diseases.	ARI-related hospitalization prevented, direct costs saved annually	Univariate sensitivity analysis	Ministry for social protection
Gao et al.46	To assess cost benefit of vaccinating employers insured under a social-health program; results extrapolated to the whole population of the city	CBA	RCT	Chinese yuan	5 y	Not reported	Respiratory system diseases and other chronic diseases such as cardiovascular diseases	Respiratory system disease and cardio-vascular diseases related hospitalization costs averted	Sensitivity analysis for vaccination coverage	Not specifically mentioned
Liu et al.47	To compare vaccinated with non-vaccinated elderly and estimate effectiveness.	CBA	RCT	Chinese yuan	6 mo	Not reported.	ILI incidence and related chronic diseases such as common cold, other respiratory tract or chronic disease such as diabetes	Medical consultations and number of hospital day-related costs averted	None performed	Not specifically mentioned
Praditsuwan et al.44	To determine cost effectiveness of influenza vaccination in the Thai elderly living in an urban community compared with placebo	CEA	RCT	Thai baht	Not reported	Not reported	ILI, upper respiratory infection, and serologically confirmed influenza.	Unclear	None performed	National Research Council of Thailand
Wongsurakiat et al.45	To determine cost- effectiveness and cost-benefit of influenza vaccination in COPD patients compared with placebo	CEA	RCT	Thai baht	16–18 mo	Not applicable	Influenza-like outcomes including episodes of acute respiratory illness	Acute respiratory infection episodes averted	None performed	National Research Council of Thailand

CBA, cost-benefit analysis; CUA, cost-utility analysis; CEA, cost-effectiveness analysis; QALY, quality adjusted life years; PSA, probabilistic sensitivity analysis; ILI, influenza-like illness.