Anderson EJ, Rouphael NG, Widge AT, et al. - By including 40 older adults, stratified by age (56 to 70 years or ≥71 years), researchers expanded a phase 1, dose-escalation, open-label trial of a messenger RNA vaccine, mRNA-1273, which encodes the stabilized prefusion SARS-CoV-2 spike protein in healthy adults, given that raised incidences of illness and mortality from coronavirus disease 2019 have been linked to older age. In a sequential manner, the participants received two doses of either 25 μg or 100 μg of vaccine given 28 days apart. In this older population, the observed adverse events related to the mRNA-1273 vaccine were predominantly mild or moderate and most frequently included fatigue, chills, headache, myalgia, and pain at the injection site. Higher binding- and neutralizing-antibody titers were shown to be induced by the 100-μg dose vs the 25-μg dose, and therefore, the use of the 100-μg dose in a phase 3 vaccine trial was supported.