Fig. 1.

Flow chart of recruitment numbers achieved in the School Infection Survey (SIS2) by school type and participants sampled during 10 November–10 December 2021 in England. *Void tests are oral fluid samples that were rejected at the processing stage prior to antibody testing, for a number of reasons, most commonly where>2 mL volume was recovered after processing (resulting in a dilution of antibody levels) or samples were incorrectly taken by participant or incorrectly packaged or transported.