The economics of routine childhood hepatitis A immunization in the United States: the impact of herd immunity.
OBJECTIVE
Because of the herd-immunity phenomenon, the benefits of immunization against hepatitis A extend beyond those received by those who are vaccinated. This analysis estimates the impact of herd immunity on the cost-effectiveness of routine hepatitis A immunization among US children.


METHODS
In an economic model, the costs and benefits of hepatitis A immunization were estimated for immunizing all US children at age 1 year over a 10-year period starting in 2005. The future burden of disease from hepatitis A was also estimated with this model, and the fraction that would be prevented by herd immunity was modeled by using a previously published analysis of the relationship between hepatitis A vaccination coverage and declines in hepatitis A incidence.


RESULTS
Without accounting for herd-immunity effects, the costs of routine immunization would average 32,000 dollars per quality-adjusted life-year gained for the first 10 cohorts immunized starting with the 2005 birth cohort. Herd-immunity effects would be expected to produce substantial additional benefits, lowering the cost of the immunization program to 1000 dollars per quality-adjusted life-year gained for the first 10 cohorts. Herd-immunity benefits would be greatest for the first few cohorts, more than doubling the benefits of immunization, and would decline over time. In a univariate sensitivity analysis, estimates were most sensitive to vaccination costs but remained below 20,000 dollars per quality-adjusted life-year under all of the assumptions.


CONCLUSIONS
Herd-immunity effects more than double the savings from hepatitis A immunization during the first 10 years of the program. After accounting for these effects, immunization is close to cost-neutral on a cost-per-quality-adjusted-life-year basis.
Armstrong
Gregory L
GL
Division of Viral Hepatitis, National Center for Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd NE, Atlanta, GA 30333, USA. garmstrong@cdc.gov
Billah
Kaafee
K
Rein
David B
DB
Hicks
Katherine A
KA
Wirth
Kathleen E
KE
Bell
Beth P
BP
D002675:Child, Preschool; D003362:Cost-Benefit Analysis; D017048:Health Care Costs; D005102:Health Expenditures; D006506:Hepatitis A / Q000191:economics* / Q000276:immunology / Q000517:prevention & control*; D006801:Humans; D032521:Immunity, Herd; D017589:Immunization Programs / Q000191:economics*; D007223:Infant; D018803:Models, Economic; D019057:Quality-Adjusted Life Years; D014481:United States; D014611:Vaccination / Q000191:economics