Collaborative Cohort of Cohorts for COVID-19 Research

C4R will leverage longitudinal data and deep phenotyping and genotyping in 14 US prospective cohort studies to ascertain all cases of COVID-19 infection, to evaluate risk factors for infection, and to track the prognosis of both those with and those without infection. The prospective studies collaborating in C4R recruited and acquired detailed pre-COVID-19 phenotyping and genotyping on a multiethnic sample of participants at field centers across the country in the last several decades.
The primary objectives for Phase 1 of the study are to 1) ascertain SARS-CoV-2 infection and COVID-19 illness by standardized questionnaires, events adjudication and serology in order to generate a community-based estimate of the incidence of COVID-19 events and an inception cohort of COVID-19 cases relatively free of referral and disease spectrum biases; 2) harmonize COVID- 19 outcomes and other relevant phenotyping across the cohorts; and 3) plan for a potential Phase 2 cross-study COVID-19 cohort for repeat measures.

Key Personnel

Elizabeth Oelsner, MD, MPH (212)
Graham Barr, MD, DrPH (212)

Primary Outcome(s)

COVID-19 questionnaire assessed at least twice by the end of one year.
Assessment of fatigue, depression, and anxiety performed at 1 or more timepoints.
Medical record ascertainment of COVID-related events, including electronic medical records (EMR).
SARS-CoV-2 seroconversions through dried blood spots.
Additional relevant phenotypic measures.


Participants in C4R are currently enrolled in 14 long-term cohort studies and range in age from young adulthood to elderly and reflect the racial/ethnic, socioeconomic, and geographic diversity of the United States.

Planned Enrollment


Power Assessment

If we conservatively estimate ascertainment in only 85% of the C4R contact target, there will be 90% power in C4R to detect an odds ratio of 1.68 per standard deviation of a continuous risk factor with respect to an event occurring in only 0.10% of participants.


Phase 1 will last 2 years and include 3 waves of questionnaires.