Evaluation of a hepatitis A immunization program

The purpose of this study was to evaluate the effectiveness of a hepatitis A vaccine requirement targeted at child-care center attendees 2-5 years of age in Maricopa County, AZ. A case-control study conducted before implementation in 1997 found that individuals with hepatitis A were 6 times more likely to have worked in or attended a child-care center than were matched controls, and 40% of hepatitis A cases were attributable to attending or working in a child-care center.

A case-control study was conducted postimplementation in 1999. Cases were individuals reported to surveillance staff between August 1, 1999 and April 30, 2000. Cases were included if they met the Centers for Disease Control and Prevention hepatitis A surveillance case definition. Each case (n = 72) was matched to 2 controls (n = 144) based on age and neighborhood.

Cases were more likely to have had contact with a hepatitis A case [odds ratio (OR), 7.04; 95% confidence interval (CI), 1.96, 25.31] than were their matched controls in the unadjusted analysis. Individuals with direct contact with a child-care center (OR 0.221; CI 0.05, 0.99) were protected against disease. In the multivariate analysis, contact with a hepatitis A case (OR 5.63; CI 1.22, 25.91) was significantly associated with disease, and the protective effect of education (OR 0.19; CI 0.06, 0.60) remained significant.

The results of this study suggest the vaccination requirement had some impact on the epidemiology of hepatitis A in Maricopa County. The risk associated with child-care centers seen in the 1997 study is no longer significantly associated with hepatitis A disease.