Figure 1. Composition and Data Collection of Self-Report and Surveillance Populations.

^aPool of individuals who contributed person-time and case counts by self-report to the center directors, according to the centers’ policies. Center directors collated weekly self-reports of positive SARS-CoV-2 test results (antigen and reverse transcription–polymerase chain reaction) and presumptive positive diagnoses of students and child care providers (CCPs) in a child care center. Date of positive test result (if applicable), date of symptom onset (if applicable), and classrooms contacted were collected. Data were deidentified for students and CCPs not enrolled in the surveillance population. From this pool, a subset enrolled in the surveillance portion of the study.

^bPool of individuals in the active surveillance population recruited from the self-report population. Contributed weekly SARS-CoV-2 testing and symptom diaries. Optional SARS-CoV-2 serology testing of students, their household contacts, and CCPs was collected.