Product- and schedule-specific vaccine effectiveness against invasive Haemophilus influenzae serotype b (Hib) disease, The Netherlands, 2005 to 2023.

BACKGROUNDInvasive Haemophilus influenzae type b (iHib) disease incidence in < 5-year-olds decreased after vaccine introduction but increased between 2011 and 2023 in the Netherlands. The National Immunisation Programme changed products in 2011 (from DTaP-IPV/Hib to DT3aP-HBV-IPV/Hib) and 2018 (to DT5aP-HBV-IPV-Hib) and schedule from 3 + 1 to 2 + 1 doses in 2020.AIMWe aimed to estimate overall, product- and schedule-specific vaccine effectiveness (VE) against iHib disease to inform vaccination strategies.METHODSWe conducted a matched case-control study extracting iHib cases born ≥ 2005 and aged 6-119 months from 2005-2023 national reference laboratory data. We selected 10 controls per case matched on birth date and sex from the population register and obtained vaccination data from the vaccination registry. Using conditional logistic regression, we estimated matched odds ratios (mOR) and VE among 6-10-month-olds (eligible only for the primary series) and 11-119-month-olds.RESULTSWe included 250 iHib cases and 2,487 controls. Among children aged 11-119 months, VE against iHib of the full schedule was 96% (95% CI: 88-99), 95% (95% CI: 91-97) and 98% (95% CI: 94-99) for any DTaP-IPV/Hib, DT3aP-HBV-IPV/Hib and DT5aP-HBV-IPV-Hib, respectively. It was 97% (95% CI: 93-99) for 2 + 1, 96% (95% CI: 93-98) for 3 + 1 doses, and > 95% for the respective primary series. No differences in VE by time since vaccination were observed between products or schedules.CONCLUSIONChanges in VE against iHib after recent product or schedule changes do not explain the increasing iHib incidence. The high VE supports pursuing optimal vaccination coverage.