In Phase 2/3, a total of 4,526 participants 6 months through 4 years of age were randomized 2:1
to receive two doses of 3 µg BNT162b2 or placebo, 3 weeks apart. The Phase 2/3 portion of the
study did not exclude participants with a history of prior SARS-CoV-2 infection or clinical
symptoms/signs of COVID-19, participants with known HIV, hepatitis B or hepatitis C, or stable
pre-existing disease (defined as disease not requiring significant change in therapy or
hospitalization for worsening disease during the 6 weeks before enrollment). Based on analyses
of post-Dose 2 safety and effectiveness data, the protocol was amended to add a third primary
series dose at least 8 weeks after Dose 2 (C4591007 protocol amendment 6). Participants
enrolled prior to implementation of protocol amendment 6 (N=3,883; February 1, 2022), were
able to be unblinded at their 6-month post-Dose 2 visit, and those originally randomized to
placebo were offered BNT162b2 vaccination at the age-appropriate dose level. Participants
enrolled after implementation of protocol amendment 6 will be unblinded at their 6-month postDose 3 visit, and those originally randomized to placebo will be offered BNT162b2 vaccination.