Several companies are working on mRNA vaccines encoding SARS-CoV-2 proteins such as the spike protein, encapsulated in nanoliposomes with specific physicochemical properties that are potentially akin to those documented for immunization against certain tumor antigens.64 The design of such nanocarriers, which will need to escape recognition by scavenger cells and to be nontoxic and nonimmunogenic, is a challenge that will require substantial time prior to clinical availability.