Figure 1. Enrollment and Matching.

Of 136,127 eligible children who had been vaccinated, 108,904 (80%) were successfully matched and included in at least one of the study groups: 94,728 were included in the vaccinated group, of whom 79,448 were originally included as members in the vaccinated group and 15,280 were initially matched as members of the unvaccinated group and then were rematched as members of the vaccinated group after receiving their first dose. A total of 29,456 children were originally included as members of the unvaccinated group but were vaccinated during the study follow-up period. Of these children, 15,280 were successfully rematched as members of the vaccinated group (for whom a new matched unvaccinated control was found); 14,176 were not. CHS denotes Clalit Health Services, PCR polymerase chain reaction, and SARS-CoV-2 severe acute respiratory syndrome coronavirus 2.