Enrolling and retaining a representative population in the NIH Researching COVID to Enhance Recovery (RECOVER)-Adult Cohort.

Background: Vulnerable populations are underrepresented in clinical studies. The design of the national RECOVER-Adult cohort study aimed to over-enroll underrepresented populations to ensure the representation of vulnerable populations in the U.S. We quantify and assess follow-up visit completion among a representative population in the RECOVER-Adult cohort. Methods: Between October 2021 and October 2023, we enrolled adult participants across 16 hub-sites in the U.S. Community outreach was used to gather and incorporate feedback prior to and during study implementation. Recruitment methods included electronic and in-person outreach by individuals trained in diversity, equity, and inclusion at health centers, health departments, and community-based organizations, as well as snowball sampling. Study staff maintained regular contact with participants between study visits via phone, email, and text, and arranged free transportation to support attendance. Results: Of the 14,880 adult participants who were enrolled in the RECOVER-Adult Cohort Study, 14,531 participants (mean[SD] age: 47.1[15.5] years, 57.0% Non-Hispanic White, 27.7% Male) completed a baseline visit. Over 85% of participants completed the first four follow-up visits, while over 90% completed a last visit. Across follow-up visits, participants who identified as minoritized groups, younger, LGBTQIA+, had less education, did not speak English, lived in a rural area, and reported a disability were less likely to complete their visits, while older and female participants were more likely to complete them. Conclusions: Our findings indicate that enrollment is more feasible than retaining a sociodemographically-representative study population, highlighting a need for innovative approaches to sustain on-going study participation in the post-pandemic era.