The global population of older adults is growing. Older adults are more vulnerable to infectious diseases compared to younger adults. Vaccines are available to protect older adults against several infectious diseases, yet their uptake remains sub-optimal. Healthcare professionals (HCP) play an important role in vaccine decisions of older adults and subsequently they could improve the vaccine uptake. This study aims to identify HCPs' awareness, attitudes and perceptions regarding older adult vaccination. Moreover, the study investigates HCPs' information needs, information seeking behaviour and factors influencing older adult vaccine communication. Semi-structured in-depth interviews were conducted with 79 HCPs involved in older adult vaccination in Hungary, Italy, the Netherlands and France. The interview guide was inspired by the Integrated Change Model (I-Change Model) and included both questions about existing vaccines and hypothetical new vaccines. All interviews were transcribed verbatim and subjected to a process of coding. Thematic analysis was performed and cross-country comparisons were made. Participants in all four countries generally shared positive views about vaccines although some reservations regarding vaccines were also shared. In case of a hypothetical new vaccine, HCPs in all countries indicated a need for information on disease and vaccine characteristics, including on efficacy, side-effects and contra-indications. The introduction of new vaccines and patient questions were drivers for information seeking among HCPs. Main sources of information used by HCPs were scientific articles and national institutes. Participants mentioned factors that could either prevent them from discussing vaccines or hamper the conversation. They expressed a desire to further develop their communication skills on vaccines. Information provision for HCPs is crucial to increase their awareness and knowledge on vaccines. However, information alone is insufficient to adequately prepare HCPs for discussing vaccines with older adults. Dedicated learning activities to acquire communication skills about vaccines are also needed.