Parental vaccine refusal, non-vaccinated children, and outbreaks of Vaccine-Preventable Diseases (VPDs) in Europe: a systematic review of aetiology and risk.

BACKGROUND: Parental vaccine hesitancy is a growing concern, and Europe has witnessed significant outbreaks of Vaccine-Preventable Diseases (VPDs) over the past two decades. Unvaccinated children are at increased risk of contracting VPDs, and the incidence of several VPDs has been on the rise. Vaccine hesitancy is a serious global health challenge. Nevertheless, the specific association between intentionally unvaccinated children and VPD outbreaks in Europe remains inadequately explored. This rapid systematic review aims to identify and examine studies focused on VPD outbreaks in Europe that involve intentionally non-vaccinated children and the factors associated with vaccine hesitancy. METHODS: A rapid systematic review was conducted with a comprehensive search of electronic databases, including Medline, Embase, and Academic Search Elite. The population, exposure and outcome (PEO) framework was used to formulate the research question, inclusion and exclusion criteria. Publications from 2010 to and including August 2023 were included. RESULTS: Of the 330 studies initially identified, a total of nine were included in the final review. The included studies indicated that unvaccinated children due to parental refusal are contributing to outbreaks of measles, diphtheria and tetanus in the European region. CONCLUSION: This systematic review provides compelling evidence of an association between intentionally unvaccinated children-those unvaccinated due to parental refusal-and outbreaks of vaccine-preventable diseases (VPDs). The findings strongly suggest that this group contributes significantly to VPD outbreaks within the European region. To deepen our understanding, further research is needed to compare the role of intentionally unvaccinated children with that of other unvaccinated groups (e.g., those unvaccinated due to medical contraindications, immunosuppression, or limited access to healthcare) in the emergence and spread of VPDs.