Under-explored assumptions in influenza vaccination models: implications for the universal vaccination of children

The association between influenza vaccination uptake and influenza and pneumonia-associated deaths in the United States

BACKGROUND

The influenza mortality burden has remained substantial in the United States (US) despite relatively high levels of influenza vaccine uptake. This has led to questions regarding the effectiveness of the program against this outcome, particularly in the elderly. The aim of this evaluation was to develop and explore a new approach to estimating the population-level effect of influenza vaccination uptake on pneumonia and influenza (P&I) associated deaths.

METHODS

Using publicly available data we examined the association between state-level influenza vaccination and all-age P&I associated deaths in the US from the 2013-2014 influenza season to the 2018-2019 season. In the main model, we evaluated influenza vaccine uptake in all those age 6 months and older. We used a mixed-effects regression analysis with generalised least squares estimation to account for within state correlation in P&I mortality.

RESULTS

From 2013-2014 through 2018-2019, the total number of all-age P&I related deaths during the influenza seasons was 480,111. The mean overall cumulative influenza vaccine uptake (age 6 months and older) across the states and years considered was 46.7%, with higher uptake (64.8%) observed in those aged ≥ 65 years. We found that overall influenza vaccine uptake (6 months and older) had a statistically significant protective association with the P&I death rate. This translated to a 0.33 (95% CI: 0.20, 0.47) per 100,000 population reduction in P&I deaths in the influenza season per 1% increase in overall influenza vaccine uptake.

DISCUSSION

These results using a population-level statistical approach provide additional support for the overall effectiveness of the US influenza vaccination program. This reassurance is critical given the importance of ensuring confidence in this life saving program. Future research is needed to expand on our approach using more refined data.

WHO guide on the economic evaluation of influenza vaccination

Influenza is responsible for substantial morbidity and mortality across the globe, with a large share of the total disease burden occurring in low- and middle-income countries (LMICs). There have been relatively few economic evaluations assessing the value of seasonal influenza vaccination in LMICs. The purpose of this guide is to outline the key theoretical concepts and best practice in methodologies and to provide guidance on the economic evaluation of influenza vaccination in LMICs. It outlines many of the influenza vaccine-specific challenges and should help to provide a framework for future evaluations in the area to build upon.

School-Based Influenza Vaccination: Health and Economic Impact of Maine's 2009 Influenza Vaccination Program

OBJECTIVE

To estimate the societal economic and health impacts of Maine's school-based influenza vaccination (SIV) program during the 2009 A(H1N1) influenza pandemic.

DATA SOURCES

Primary and secondary data covering the 2008-09 and 2009-10 influenza seasons.

STUDY DESIGN

We estimated weekly monovalent influenza vaccine uptake in Maine and 15 other states, using difference-in-difference-in-differences analysis to assess the program's impact on immunization among six age groups. We also developed a health and economic Markov microsimulation model and conducted Monte Carlo sensitivity analysis.

DATA COLLECTION

We used national survey data to estimate the impact of the SIV program on vaccine coverage. We used primary data and published studies to develop the microsimulation model.

PRINCIPAL FINDINGS

The program was associated with higher immunization among children and lower immunization among adults aged 18-49 years and 65 and older. The program prevented 4,600 influenza infections and generated $4.9 million in net economic benefits. Cost savings from lower adult vaccination accounted for 54 percent of the economic gain. Economic benefits were positive in 98 percent of Monte Carlo simulations.

CONCLUSIONS

SIV may be a cost-beneficial approach to increase immunization during pandemics, but programs should be designed to prevent lower immunization among nontargeted groups.

The cost-effectiveness of influenza vaccination in elderly Australians: an exploratory analysis of the vaccine efficacy required

It is important to consider the value for money offered by existing elderly influenza vaccination programs, particularly as doubts persist about the magnitude of the effectiveness of such programs. An informative approach to explore the value of vaccination is to consider what vaccine efficacy would be required for a program to be considered cost-effective. To estimate the cost-effectiveness of the current elderly (65+ years) influenza vaccination program in Australia, we modelled how the hypothetical removal of vaccination would increase current disease burden estimates depending on alternative vaccine efficacy assumptions. The base-case results of the analysis found that the existing elderly vaccination program is likely to be cost-effective (under A$50,000 per quality-adjusted life year gained) if the vaccine efficacy is above ∼30%. This study offers reassurance that the influenza vaccination of elderly Australians is likely to offer value for money.

Understanding the cost-effectiveness of influenza vaccination in children: methodological choices and seasonal variability

BACKGROUND

The universal vaccination of children for influenza has recently been recommended in the UK and is being considered in other developed countries.

OBJECTIVES

The aim of this study was to explore the potential costs and benefits of childhood influenza vaccination to gain a better understanding of the key drivers of cost-effectiveness.

METHODS

As our case study we examined the cost-effectiveness of vaccination in Australian schoolchildren using an age-stratified Susceptible Exposed Infectious Recovered model.

RESULTS

The results of this study highlight the critical role that methodological choices play in determining the cost-effectiveness of influenza vaccination. These choices include decisions about the structure of the model (including/excluding herd immunity) and what costs and benefits to include in the analysis. In scenarios where herd protection was included we estimated that the program was likely to be cost-effective. The study also illustrates the importance of the inherent seasonal variability of influenza, which can produce counter-intuitive results, with low transmission seasons being easier to control by vaccination but resulting in fewer benefits.

CONCLUSIONS

Universal childhood influenza vaccination is likely to be cost-effective if a substantial herd protection effect can be achieved by the program. However, it is important that decision makers understand the role of seasonal variability and the impact of alternative methodological choices in economic evaluations of influenza vaccination.