BDV booster decision visit, FPFV first participant first visit, PDV participant decision visit. Participants (n = 29,035) who started the open-label observational phase include those who had a PDV or unblinding date. In Part B, 12,554 of the 12,649 participants in the placebo-mRNA-1273 group who received a first injection of mRNA-1273 also received a second dose. Of the 15,185 participants in the mRNA-1273 group who received at least one injection of mRNA-1273 in Part A, 139 received one injection of mRNA-1273 in Part B. One participant discontinued after the discontinuation cutoff date. A greater proportion of participants in the placebo compared with the mRNA-1273 group discontinued the study due to protocol deviations, primarily receipt of an off-study COVID-19 vaccine. The higher number of discontinuations by the withdrawal of consent in the mRNA-1273 group is explained largely by the recruitment of participants to other booster dose clinical studies (~3863 participants to phase 2 [NCT04405076] and phase 2/3 [NCT05249829] studies). Participants were considered to have completed the study if they completed the final visit on day 759 (month 25), 24 months following the last injection of study vaccination. ** Included one participant who did not enter the open-label observational phase. Included 10 participants who did not enter the open-label observational phase. Study initiation dates: for Part A blinded FPFV July 27, 2020; for Part B (PDV) December 2020; Part C (BDV) September 23, 2021. Data-cutoff date: Part A March 26, 2021; Part B Booster day 1 visit or database lock date, April 7, 2023, whichever is earlier; database lock date: Part C April 7, 2023.
