Vaccine hesitancy refers to the delay in acceptance or refusal of vaccination despite the availability of vaccination services. It is complex and context-specific, varying across time, place, and vaccines. It is influenced by factors such as complacency, convenience, and confidence. The term "vaccine hesitancy" was chosen over "vaccination hesitancy" as it is more commonly used and reflects the broader range of immunization concerns. Vaccine hesitancy is a behavioral phenomenon that is vaccine and context-specific, and is measured against an expectation of reaching a specific vaccination coverage goal. The Vaccine Hesitancy Determinants Matrix categorizes factors influencing vaccine acceptance, delay, or rejection into three categories: contextual, individual and group, and vaccine-specific influences. The "3 Cs" model highlights three categories: complacency, convenience, and confidence. Vaccine hesitancy is not solely determined by communication, although poor communication can negatively influence vaccination uptake. The Working Group concluded that a practical definition of vaccine hesitancy is needed to ensure that Immunization Programme Managers, policy makers, clinicians, and researchers consistently use a standard term to cover the broad range of factors causing low vaccination uptake. The definition of vaccine hesitancy is that it refers to delay in acceptance or refusal of vaccination despite the availability of vaccination services. It is complex and context-specific, varying across time, place, and vaccines. It is influenced by factors such as complacency, convenience, and confidence. The Working Group also emphasized the importance of developing targeted communication strategies to address hesitancy issues and improve vaccination uptake.Vaccine hesitancy refers to the delay in acceptance or refusal of vaccination despite the availability of vaccination services. It is complex and context-specific, varying across time, place, and vaccines. It is influenced by factors such as complacency, convenience, and confidence. The term "vaccine hesitancy" was chosen over "vaccination hesitancy" as it is more commonly used and reflects the broader range of immunization concerns. Vaccine hesitancy is a behavioral phenomenon that is vaccine and context-specific, and is measured against an expectation of reaching a specific vaccination coverage goal. The Vaccine Hesitancy Determinants Matrix categorizes factors influencing vaccine acceptance, delay, or rejection into three categories: contextual, individual and group, and vaccine-specific influences. The "3 Cs" model highlights three categories: complacency, convenience, and confidence. Vaccine hesitancy is not solely determined by communication, although poor communication can negatively influence vaccination uptake. The Working Group concluded that a practical definition of vaccine hesitancy is needed to ensure that Immunization Programme Managers, policy makers, clinicians, and researchers consistently use a standard term to cover the broad range of factors causing low vaccination uptake. The definition of vaccine hesitancy is that it refers to delay in acceptance or refusal of vaccination despite the availability of vaccination services. It is complex and context-specific, varying across time, place, and vaccines. It is influenced by factors such as complacency, convenience, and confidence. The Working Group also emphasized the importance of developing targeted communication strategies to address hesitancy issues and improve vaccination uptake.