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

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.

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.

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.

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.