Transmission of hepatitis A through household contact.

In the USA, cost effectiveness assessments support childhood hepatitis A vaccination in geographical areas with elevated disease rates, but not nationally. However, these studies do not address the reduction in disease transmission which may result from routine childhood vaccination. Using decision analysis, we estimated the number and age distribution of secondary hepatitis A cases occurring within households with an index case. Based on the age of the index case, we determined household size and age composition, the proportion of household members susceptible to hepatitis A, the probability of disease transmission, and the likelihood secondarily infected household members would exhibit symptoms. Our model indicates that for every 100 index cases age 6-11 years, 47.2 secondary infections would occur within households, with 23.1 causing overt disease. Lower transmission rates for older index cases reflect smaller household sizes and a higher proportion of household contacts with hepatitis A immunity. When disease transmission rates are applied to a model simulating lifetime risks of hepatitis A, universal vaccination of an annual USA birth cohort is estimated to prevent 24 100 cases of overt disease among household contacts in addition to 71 000 cases among vaccinees. Sensitivity analysis provides a wide range of estimates, but even conservative assumptions suggest routine vaccination would yield an important reduction in secondary cases. Evaluations of hepatitis A prevention should consider the ability of immunization to protect household and other personal contacts.