The Collaborative Cohort of Cohorts for COVID-19 Research, or C4R, is a nationwide study of more than 50,000 individuals to determine factors that predict disease severity and long-term health impacts of COVID-19. 

Participants in C4R, who are currently enrolled in 14 long-term cohort studies, range in age from young adulthood to elderly and reflect the racial/ethnic, socioeconomic, and geographic diversity of the United States. Many C4R participants have been followed for decades, providing a vast amount of data from imaging tests, physiologic assessments, and genomic analyses. C4R is designed to understand how and why these participants are at varying risk of SARS-CoV-2 infection and illness, as well as to understand the health effects of social and economic changes experienced during the COVID-19 pandemic.