This supplementary appendix provides additional information about the Phase 1–2 trial of a SARS-CoV-2 recombinant spike protein nanoparticle vaccine (NVX-CoV2373) conducted by Keech et al. in the *New England Journal of Medicine*. It includes details on the study team members from various institutions, vaccination pause rules, RT-PCR testing assays, immunologic assay methods, cellular immune responses, convalescent sera description, safety laboratory abnormalities, unsolicited adverse events, and supplemental figures and tables. The appendix highlights the safety and efficacy of the vaccine, including the incidence of adverse events, laboratory abnormalities, and immune responses in participants. It also provides detailed methods for assessing immune responses and discusses the results of the trial, including seroconversion and serorecovery rates.This supplementary appendix provides additional information about the Phase 1–2 trial of a SARS-CoV-2 recombinant spike protein nanoparticle vaccine (NVX-CoV2373) conducted by Keech et al. in the *New England Journal of Medicine*. It includes details on the study team members from various institutions, vaccination pause rules, RT-PCR testing assays, immunologic assay methods, cellular immune responses, convalescent sera description, safety laboratory abnormalities, unsolicited adverse events, and supplemental figures and tables. The appendix highlights the safety and efficacy of the vaccine, including the incidence of adverse events, laboratory abnormalities, and immune responses in participants. It also provides detailed methods for assessing immune responses and discusses the results of the trial, including seroconversion and serorecovery rates.