This Phase II clinical trial, sponsored by the Ministerio de Salud de Ciudad Autónoma de Buenos Aires, aims to evaluate the immunogenicity and safety of heterologous SARS-CoV-2 vaccine regimens in a population that has previously received a dose of the Gam-COVID-Vac vaccine. Given the logistical challenges in vaccine distribution and the emergence of new variants, the trial addresses a critical public health need in Argentina, where a significant number of individuals are partially vaccinated. If successful, the results could support the adoption of heterologous vaccination strategies, potentially expanding the market for vaccine manufacturers involved in the study and enhancing public health responses to COVID-19. The competitive landscape may shift as data emerges regarding the efficacy of these combinations, influencing future vaccine development and approval processes.