Late initiation of pneumococcal and Haemophilus influenzae type b vaccinations.

Introduction: For children who initiate a vaccine series late, the Centers for Disease Control and Prevention (CDC) provides a catch-up schedule to guide providers in achieving full vaccination. Typically, the routine and catch-up schedules recommend the same number of doses for series completion. However, children starting pneumococcal (PCV) or Haemophilus influenzae type b (Hib) vaccination at or after 7 months often require fewer doses than earlier initiators. We aimed to quantify late PCV and Hib series initiators and determine series completion within CDC catch-up guidelines.

Methods: This cross-sectional study analyzed vaccine records from the 2016-2021 National Immunization Survey-Child. We quantified the prevalence of and identified characteristics of children who initiated the PCV or Hib series at or after age 7 months (215 days). We evaluated late initiators' series completion based on age of series initiation and when subsequent doses were received.

Results: Of 99,652 children, 2.5 % (95 % CI: 2.2-2.7 %) and 2.3 % (95 % CI: 2.1-2.5 %) of U.S. children initiated PCV or Hib series late, respectively. The median age of late series initiation was 384 days for PCV and 407 days for Hib. Overall, 34.9 % (95 % CI: 29.9-39.9 %) of late PCV initiators, and 26.3 % (95 % CI: 21.2-31.4 %) of late Hib initiators, received other vaccines from age 6 weeks to <7 months. Late PCV initiation decreased from 2.9 % (95 % CI: 2.4-3.4 %) in 2016 to 1.7 % (95 % CI: 1.3-2.1 %) in 2021. About 77.4 % (95 % CI: 69.0-83.9 %) of late PCV (routine 4-dose series) and 87.5 % (95 % CI: 76.3-93.3 %) of late Hib (routine 4-dose series) initiators completed the series per catch-up guidelines.

Conclusions: A subset of U.S. children initiated the PCV or Hib series at or after 7 months, and most had not received other recommended vaccines between 6 weeks and 7 months-underscoring the need for evidence-based interventions that support early access to primary care.