Variation in hepatitis B immunization coverage rates associated with provider practices after the temporary suspension of the birth dose

Abstract

Background: In 1999, the American Academy of Pediatrics and U.S. Public Health Service recommended suspending the birth dose of hepatitis B vaccine due to concerns about potential mercury exposure. A previous report found that overall national hepatitis B vaccination coverage rates decreased in association with the suspension. It is unknown whether this underimmunization occurred uniformly or was associated with how providers changed their practices for the timing of hepatitis B vaccine doses. We evaluate the impact of the birth dose suspension on underimmunization for the hepatitis B vaccine series among 24-month-olds in five large provider groups and describe provider practices potentially associated with underimmunization following the suspension.

Methods: Retrospective cohort study of children enrolled in five large provider groups in the United States (A-E). Logistic regression was used to evaluate the association between the birth dose suspension and a child's probability of being underimmunized at 24 months for the hepatitis B vaccine series.

Results: Prior to July 1999, the percent of children who received a hepatitis B vaccination at birth varied widely (3% to 90%) across the five provider groups. After the national recommendation to suspend the hepatitis B birth dose, the percent of children who received a hepatitis B vaccination at birth decreased in all provider groups, and this trend persisted after the policy was reversed. The most substantial decreases were observed in the two provider groups that shifted the first hepatitis B dose from birth to 5-6 months of age. Accounting for temporal trend, children in these two provider groups were significantly more likely to be underimmunized for the hepatitis B series at 24 months of age if they were in the birth dose suspension cohort compared with baseline (Group D OR 2.7, 95% CI 1.7-4.4; Group E OR 3.1, 95% CI 2.3-4.2). This represented 6% more children in Group D and 9% more children in Group E who were underimmunized in the suspension cohort compared with baseline. Children in the reversal cohort in these groups remained significantly more likely to be underimmunized compared with baseline. In contrast, in a third provider group where the typical timing of the third dose was unchanged and in two other provider groups whose hepatitis B vaccination schedules were unaffected by the birth dose suspension, hepatitis B vaccination coverage either was maintained or improved.

Conclusion: When the hepatitis B birth dose was suspended, provider groups that moved the first dose of vaccination to 5-6 months of age or later had decreases in hepatitis B vaccine coverage at 24 months. These findings suggest that as vaccine policy changes occur, providers could attempt to minimize underimmunization by adopting vaccination schedules that minimize delays in the recommended timing of vaccine doses.

Figure 1

Calculation of predicted absolute differences in percent of 24-month-olds underimmunized for the hepatitis B vaccine series, birth dose suspension and reversal periods versus baseline. --- : % children underimmunized based on logistic regression model and the observed data. - - - - : % children underimmunized predicted from the baseline. Time point a: July 1999 birth cohort, start of the birth dose suspension period. Δ₁ compares % children underimmunized for the July 1999 birth cohort based on the fitted data to that predicted from the baseline. Time point b: October 1999 birth cohort, following reversal of the birth dose suspension. Δ₂ compares % children underimmunized for the hepatitis B vaccine series for the October 1999 birth cohort based on the fitted data to that predicted from baseline.

Figure 2

Percent of children enrolled in five large U.S. provider groups who received a first hepatitis B vaccination within the first week of life, October 1996 – December 1999. Baseline cohort: born between October 1996 – June 1999 (n = 67,835). Birth dose suspension cohort: born between July 1999 – September 1999 (n = 6,401). Reversal cohort: born between October 1999 – December 1999 (n = 6,065).

Figure 3

Delays in age at receipt of hepatitis B vaccine doses among children enrolled in provider groups D and E following the hepatitis B birth dose suspension recommendations, baseline cohort vs. birth dose suspension cohort. - - - : Baseline cohort of children born between October 1996 – June 1999 (n = 67,835). : Birth dose suspension cohort of children born between July – September 1999 (n = 6,401). Age at vaccination was grouped into the following categories: birth (0–7 days), < 2 months (8 days – 2 months), 3–4 months, 5–6 months, 7–8 months, 9–10 months, 11–12 months, 13–14 months, 15–16 months, 17–18 months, 19–20 months, 21–24 months, and did not receive dose by 24 months ("never").