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Purpose: Evaluate five different recruitment strategies for their capacity to enroll and retain both healthy and vulnerable older adults as part of a multiyear influenza vaccination study. Methods: We analyzed recruitment methods and other characteristics of individuals who participated in or were considered for five sequential one-year studies. Results: Of 940 screened individuals, 820 met eligibility criteria with 795 enrolled over the five-year study (307 primary participants). Among these enrollees, 63.4% were female and 95.5% were white, with mean ages of 75.3 (older group) and 30.6 (younger group). More than a half (56.7%) of the participants enrolled more than once, participating an average of 2.56 (SD=1.6) times. The majority (81.9%) of individuals recruited each year were return participants identified during earlier recruitments. Physician referrals resulted in only 5.3% recruitments. Conclusions: Recruitment and retention of study subjects, especially older adults, was facilitated by the existence of a database listing past participants.