Vaccinations are not associated with inhibitor development in boys with severe haemophilia A

Inhibitor development in previously untreated patients (PUPs) with severe haemophilia A is a multifactorial event. It is unknown whether paediatric vaccinations given in close proximity to factor VIII (FVIII) are associated with inhibitor development. To assess whether paediatric vaccinations in close proximity to FVIII within the first 75 exposure days (EDs) are associated with inhibitor development in PUPs with severe haemophilia A. We included 375 PUPs with severe haemophilia A ( <0.01 IU/mL) from the PedNet Registry who had received vaccinations between the first and 75th ED or inhibitor development. Inhibitor risk was compared between patients who did and who did not receive vaccinations within 24, 72 or 120 hours of FVIII infusion. Unadjusted and adjusted hazard ratios were calculated for any or repeated vaccinations in close proximity to FVIII, using Cox regression. Inhibitor development occurred in 77 of 375 patients (20.5%). Overall inhibitor development appeared similar or lower in patients receiving vaccinations in close proximity to FVIII as compared to patients receiving vaccinations without FVIII: for 24 hours, this was 19.2% and 21.4% (P = .186), for 72 hours, 16.4% and 27.3% (P = .023) and for 120 hours, 18.3% and 25.0% (P = .085), respectively. We found no association between vaccinations given in close proximity to FVIII exposure within the first 75 EDs and inhibitor development. Our data do not support avoiding administration of FVIII at time of routine vaccinations