This study assesses whether combining information about diseases and sequelae supports learning about disease risks and influences related health behavior (vaccination). Objective: To test whether extending knowledge about the risks of primary diseases (e.g., influenza) with causally linked secondary diseases (sequelae such as sepsis) can decrease vaccine hesitancy in older adults, who are especially vulnerable to primary and secondary diseases. Method: In a preregistered longitudinal online experiment, 585 German participants > 60 years of age were randomly assigned to a 3 (time: before and after leaflet presentation, 3-month follow-up; within) × 3 (educational leaflet type: sepsis leaflet, traditional vaccination leaflet, and control leaflet; between) mixed-measurements design. The assessed outcomes were knowledge about influenza, pneumococci, and sepsis; risk perceptions; and immediate and long-term vaccination intention and behavior for pneumococcal and influenza vaccinations. Results: The sepsis leaflet immediately increased the knowledge about influenza (effect size, η² = .080), pneumococci (η² = .071) and sepsis (η² = .113), risk perceptions (η² = .007), and intentions for both vaccinations (both η² = .015). Behavior during the follow-up did not differ between the conditions. Additional mediation analysis showed that increased knowledge immediately after the experiment predicted increased risk perceptions and intentions 3 months later (binfluenza = .060; bpneumococci = .055). Conclusion: Because immediate increases in knowledge and risk perceptions did not change behavior in the long term, extended knowledge interventions might be more effective in locations where positive intention can directly turn into action, such as doctors’ clinics. (PsycInfo Database Record (c) 2021 APA, all rights reserved)