The COVID-19 Schools Infection Survey (SIS) aimed to investigate the prevalence of current coronavirus (COVID-19) infection and presence of antibodies to COVID-19 among pupils and staff in a sample of primary and secondary schools in England. SIS was carried out in the 2020/21 academic year in a sample of schools from 15 local authorities in England. The survey over sampled local authorities in the North West (where COVID-19 prevalence was highest when the survey was initially rolled out). Results are not representative of England as a whole. Files contain lab data (antigen test results, staff antibody test results and pupil antibody test results), questionnaire data (enrolment, extended, follow-up, vaccine surveys, end of survey, headteacher extended and headteacher follow-up questionnaires), and schools data. Repeated surveys are being carried out to collect risk factor information together with virus and antibody samples in a cohort of pupils and staff.