In July 1999, the longstanding preference to begin hepatitis B vaccination
of all US infants at birth was temporarily suspended because of concerns about
exposure to mercury contained in the vaccine preservative thimerosal. The
suspension was lifted in September 1999 when preservative-free hepatitis B
vaccine became available.
To determine the effects of changes in recommendations regarding administration
of a hepatitis B birth dose on vaccination coverage.
Design, Setting, and Participants
Cohort analysis of vaccination status of 41 589 US children born
before, during, and after the recommendation to suspend the birth dose.
Main Outcome Measures
Association between birth cohort and age at receipt of hepatitis B vaccine
dose 1, and receipt by 19 months of age of all recommended vaccines.
The proportion of US infants who received dose 1 of hepatitis B vaccine
at birth declined from 47% among those born 7 to 12 months before the suspension
to 11% among those born during the suspension. Birth-dose coverage remained
significantly lower in the year after the suspension was lifted (23% in the
first 6 months and 33% in months 7-12). Coverage with 3 doses of hepatitis
B vaccine by 19 months of age declined from 88% among those born 7 to 12 months
before the suspension to 81% among those born during the suspension and 85%
among those born in the 6 months after the suspension, but returned to baseline
levels for those born 7 to 12 months after the suspension was lifted. These
reductions represent 750 000 fewer newborns vaccinated during 2000 compared
with 1998, and an excess 182 000 children undervaccinated for hepatitis
B at 19 months of age compared with 1998 coverage levels. Coverage with other
recommended vaccinations did not decline over this time.
Reductions in hepatitis B vaccine birth-dose coverage persisted after
recommendations were made to resume previous newborn vaccination practices.
Although the recommendation to complete the series by 19 months of age was
never changed, infants born between July and December 1999 were less likely
to have completed the series by 19 months, compared with infants born during
the previous year. The lack of impact on other vaccinations suggests that
public confidence in immunization remained strong.