The shadow of reactogenicity: Parental hesitancy due to prior vaccine experiences

Vaccination has dramatically reduced the global burden of pediatric vaccine-preventable diseases, yet a decline in immunization rates in recent years has led to the re-emergence of diseases once nearing eradication, such as measles and pertussis. This trend is of particular concern for children with chronic conditions or those who are immunocompromised, as they face elevated risks of severe illness and complications. Parental vaccine hesitancy (PVH) plays a central role in this decline and is a multifactorial phenomenon shaped by demographic and socioeconomic factors, the child's health condition, parental attitudes and personal experiences, perceived disease risk and trust in the government and healthcare system. This targeted literature review demonstrates a consistent association between prior experiences of vaccine reactogenicity among parents or caregivers and subsequent hesitancy to vaccinate their children. Even mild or anticipated adverse events following immunization (AEFIs) can trigger emotional aversion or anxiety, lead to overestimation of the likelihood and severity of future reactions, erode trust in the healthcare system and vaccine safety information, and open susceptibility to anti-vaccine rhetoric, particularly when experienced by parents or their children. These experiences often outweigh clinical evidence in shaping vaccine decisions and contribute to long-term hesitancy. Addressing PVH requires a multifaceted approach. Healthcare providers must engage in empathetic, transparent communication, offering clear information about expected side effects and differences in vaccine platforms. Where feasible, offering less reactogenic vaccine options may help mitigate concerns. Additionally, proactively optimizing vaccine formulations for low reactogenicity in early development could reduce downstream hesitancy and improve public confidence. By acknowledging the emotional and experiential dimensions of PVH, public health strategies can better support informed parental decision-making and improve vaccine uptake in vulnerable pediatric populations.