Cost of cost-sharing: The impact of Medicaid benefit design on vaccination coverage rates

Background. Prior research indicates lack of insurance coverage and cost-sharing reduce use of preventive services among low-income persons. State Medicaid benefits policy may affect uptake of recommended adult vaccinations.

Objectives. We examined the impact of three aspects of Medicaid benefit design (coverage for particular vaccines, permitting cost-sharing, and copayment amounts) on uptake of vaccinations in the fee-for-service Medicaid population of adults 18-64 years old.

Methods. We combined previously published reports to obtain state Medicaid policy information from 2003 and 2012.  Data on influenza and pneumococcal vaccination coverage rates were taken from the Behavioral Risk Factor Surveillance System, a nationally representative survey of non-institutionalized US adults.  We used a differences-in-differences framework to estimate the effect of copayment charges, allowing cost-sharing, or covering the vaccine in the Medicaid program on vaccination coverage.  We controlled for year by year changes and state level differences in vaccination rates. Since Medicaid eligibility thresholds differ for pregnant women and childless adults, we examined these populations separately.

Results. Each additional dollar of copayment for vaccination decreased influenza vaccination rates between 2 and 10 percentage points and pneumococcal vaccination rates by approximately 1 percentage point.  Results for covering the vaccine or permitting cost sharing were mixed.

Conclusions. Imposing copayments for vaccination is associated with lower vaccination rates. This is one of the first studies to demonstrate this association among adult Medicaid beneficiaries.