Hospital-based surveillance of vaccine-preventable diseases in children: a retrospective study in a Dutch tertiary hospital (2024–2025).

Background
Vaccine-preventable diseases (VPDs) are a major cause of morbidity in children, despite established immunization programs. Surveillance of VPDs is essential to inform public health strategies and strengthen national immunization programs. This pilot study evaluated the feasibility of using routinely collected hospital data for in-hospital surveillance of pediatric VPDs.

Methods
We performed a retrospective cohort study at a tertiary hospital in the Netherlands from July 2024 to June 2025, before national implementation of RSV immunization. Children <18 years admitted with laboratory-confirmed infections caused by pathogens with available licensed vaccines were included, regardless of inclusion in the national immunization program. Feasibility was assessed based on case ascertainment, completeness of key variables and availability of vaccination information.

Results
We included 99 children (103 VPD episodes; median age 0.6 years), of whom 60% (n = 59) required pediatric intensive care. Most hospitalizations were caused by respiratory infections, particularly RSV (n = 52) and influenza (n = 27). Case ascertainment required integration of multiple data sources, as 45% of children were tested outside the study hospital. Clinical variables were largely complete and vaccination status could be determined for 84% of episodes. Overall, 9% (n = 9) of VPD episodes occurred in fully vaccinated children. Most VPD episodes (76%; n = 78) occurred in children not vaccinated against the specific pathogen, mainly because they were too young or because the pathogen or serotype was not covered by the national immunization program or current guidelines.

Conclusions
Retrospective hospital-based surveillance of pediatric VPDs is feasible and provides key information to guide efforts to optimize the national immunization program. By capturing disease severity and vaccine preventability, it complements existing surveillance data in the Netherlands.