Layton JB, Butler AM, Brookhart MA, Panozzo CA. Variation in rotavirus vaccination coding in US State Medicaid data. Presented at the 35th Annual ICPE Conference; August 28, 2019. Philadelphia, PA. [abstract] Pharmacoepidemiol Drug Saf. 2019 Aug 20; 28(S2):852. doi: 10.1002/pds.4864.

BACKGROUND:  US state Medicaid claims databases may be an attractive option for research into childhood vaccination use, safety, or effectiveness. However, variation in state Medicaid reimbursement policies and coding practices may present challenges for vaccination research using state Medicaid data. Rotavirus vaccines are the only oral vaccine licensed for US infants, thus providing a useful test case for exploring differences in the use of vaccine-specific procedures codes versus oral administration codes.

OBJECTIVE: We quantify state-specific differences in procedure coding for rotavirus vaccination in Medicaid programs by identifying rotavirus vaccine–specific codes and oral vaccine administration codes.

METHODS:  We identified infants born between January 1 and June 30, 2010 in four US states’ (California, Georgia, North Carolina, Texas) Medicaid programs. We identified all rotavirus vaccine–related claims in the cohort during the first 6 months of life and categorized each claim as either vaccine-specific or vaccine administration. As one vaccination could result in multiple codes of different types, we defined unique vaccination events as discrete 7-day periods during which at least one rotavirus-related vaccine code was present; all codes occurring in the period were assumed to result from the same vaccination event. We calculated the state-specific proportions of eligible newborns with rotavirus vaccination claims, overall and by state, and described the code types used in each state.

RESULTS: We identified 259,857 unique vaccination events arising from 273,312 eligible newborns. 59.4% of children had ≥1 rotavirus vaccine-related code in the first 6 months of life. The proportion of vaccinated children with vaccine-specific and oral vaccine administration codes differed substantially across states: California and Georgia used vaccine-specific codes almost exclusively (96.7% and 99.1%,); North Carolina had only oral vaccine administration codes (>99.9%); Texas had a mixture (32.1% vaccine-specific codes alone, 40.0% oral vaccine administration codes alone, and 27.9% had both).

CONCLUSIONS: Rotavirus vaccination coding varied substantially across states. Vaccine-specific codes were not used in all states, and Medicaid data in states without (or with incomplete) vaccine-specific coding may be infeasible for vaccine research as specific vaccine types may not be identifiable from administration codes alone. Investigators should carefully evaluate state Medicaid policies and patterns of vaccination uptake, as vaccine reimbursement policies and availability of vaccine claims may vary.

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