Perinatal hepatitis B transmission and vaccination timing in a managed care cohort: assessment of the temporary delay in newborn hepatitis B vaccination due to thimerosal content.

BACKGROUND

From July to September 1999, due to a concern of toxicity from exposure to thimerosal-containing vaccines, the American Academy of Pediatrics and U.S. Public Health Service temporarily recommended delaying the administration of first dose of hepatitis B vaccine until the age of 2-6 months for infants born to hepatitis B surface antigen negative mothers. Our objectives were to determine whether the recommendation affected the rate of perinatal hepatitis B infection in a multistate managed care population; to describe neonatal and early childhood cases of hepatitis B infection and to evaluate a possible role of the recommendation; and to assess the timeliness, with respect to the U.S. childhood immunization schedule, of vaccinations during the first 2 years of life.

METHODS

We identified 3 cohorts of infants born before (July 1998 to June 1999), during (July 1999 to September 1999) and after (October 1999 to September 2000) the recommendation period. We used automated claims data to identify possible neonatal and early childhood hepatitis B cases using specific ICD-9 diagnosis and CPT procedure codes and validated cases through medical record review. Using Health Plan Employer Data and Information Set (HEDIS) data, we calculated vaccination coverage for the first dose of hepatitis B vaccine at 3-month intervals from January 1999 to September 2000.

RESULTS

The eligible populations in the "before," "during" and "after" cohorts were 29,347, 7791 and 29,215 infants, respectively. Of 41 possible hepatitis B cases identified in the 3 cohorts, we confirmed 1 case in the after cohort with medical record review. Despite receiving the first dose of hepatitis B vaccine and hepatitis B immunoglobulin within 12-24 hours of birth, the infant was diagnosed with laboratory-confirmed chronic hepatitis B at age of 9 months. An analysis of HEDIS data showed that vaccination coverage for the first dose of hepatitis B vaccine was 98% (January to March 1999) and 96% (April to June 1999) for the "before" cohort and 66% for the "during" cohort. For the "after" cohort the coverage was 72% (October to December 1999), 83% (January to March 2000), 91% (April to June 2000) and 95% (July to September 2000).

CONCLUSIONS

This study did not identify any perinatal hepatitis B transmission among health plan enrollees associated with the 1999 recommendation. The recommendation did result in a delay of hepatitis B birth dose in the "during" cohort as intended for infants born to hepatitis B surface antigen negative mothers. Six months after the recommendation was rescinded there was still a delay in the timing of first dose of hepatitis B vaccine, but the timing had returned to the prerecommendation level after 9-12 months.