Key issues for estimating the impact and cost-effectiveness of seasonal influenza vaccination strategies

Figures & data

Table 1. Stages in establishing the impact of seasonal influenza vaccination

Stage	Key components	Potential difficulties	Available data and tools
1. Establish the influenza-attributable disease burden.	Community (non-health seeking) infection	Cases are not generally recorded	Serological and virological surveys combined with statistical and mathematical models
	Healthcare utilization and mortality	Cases have non-specific symptoms and are rarely tested	Longitudinal data sets Statistical time-series models
2. Establish the economic burden of influenza.	Direct costs to healthcare providers and households	Volume estimates of outcomes must be matched with unit costs	Health care records Patient surveys Market prices (or shadow prices), tariffs
	Indirect costs (loss of productivity and leisure time)	Estimates differ widely depending on the method used and inter-country differences in work absenteeism.	Human capital estimates Friction costs Stated or revealed preference studies
3. Establish vaccine impact in a population	Efficacy in vaccinated individuals	Clinical trials estimates vary due to changes in subtype prevalence, vaccine match and case ascertainment	Randomized clinical trials Meta-analyses
	Indirect impact on non-vaccinated individuals	Indirect protection depends on setting-specific variables that are difficult to directly measure	Household and cluster randomized studies Transmission dynamic models

Table 2. Key issues considered in economic evaluations of seasonal influenza vaccination

				Key issues relating to outcomes*
Paper	Target group	Number of studies reviewed	Main study conclusions	Herd	Endp	Prod	VCost	VEff	Other key issues
Newall 2012^17	Children ≤ 18 y	20	11/20 cost saving; remainder mostly cost-effective	√	√	√	√		Difficulty estimating severe outcomes.
Coleman 2006^46	Children	7	Not discussed	√		√			Consumer choice Direct expenses paid by households Trade-off between paying for prevention and treatment
Nichol 2011^47	Children ≤ 18 y	20	11/20 cost saving; remainder mostly cost-effective	√
Savidan 2008^48	Children < 18 y	15	All cost saving or cost-effective	√			√	√
Burls 2006^52	Healthy adults, healthcare workers	14	10/14 cost saving (including 2/2 on health care workers)	√
Gatwood 2012^49	Healthy adults 18–64 y	7	“Generally not cost saving”			√		√	Variability in outcomes Setting of vaccine delivery Severe adverse events Estimating less severe endpoints
Hogan 2012^50	Healthy adults	10	8/10 favored vaccination	√	√		√	√	Perspective (employer only or employee as well)
Newall 2009^51	Adults 50–64 y	6	All cost-effective		√	√	√	√	Life expectancy in people with co-morbidities
De Waure 2012^45	Adults > 50 y and high-risk populations	20	All cost saving or cost-effective in both elderly and high-risk groups	√		√
Postma 2006^53	Elderly	18	15/18 cost saving, 16/18 cost-effective			√	√	√	Definition of influenza-attributable hospitalisation or death

* Herd: herd protection; Endpt: mismatch in endpoints used to estimate incidence and vaccine effectiveness (e.g., acute respiratory illness, influenza-like illness, laboratory-confirmed influenza); Prod: productivity loss due to influenza; VCost: drivers of vaccination costs (purchase and administration); VEff: drivers of vaccine effectiveness.

Table 3. Specific recommendations for estimating the impact and cost-effectiveness of seasonal influenza vaccination in particular groups

Target group	Recommendations
Healthy young children (0–5 y)	Consideration of household and pre-school transmission is important in this key transmission group.
Healthy school age children	Consideration of household and school-based transmission is important in this key transmission group.
Healthy adults	This is not a usual target group for seasonal influenza vaccination. However, the economic burden of influenza to families and employers may be substantial due to its effect on productivity.
Elderly	Account needs to be taken of the substantial burden of morbidity and mortality that may not necessarily be attributed to influenza.
Population with high risk of complications due to chronic conditions	Appropriate assessment of the risk and vaccine effectiveness in these groups, which are often small in comparison with the overall population.
Pregnant women	Potential protective effect mothers on their infants should be considered.
Health care workers	Potential protective effect on high-risk patients should be considered.

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