The goal of this study was to explore the antibody response in individuals with solid organ transplants after their second SARS-CoV-2 vaccine dose in the United States. Eligible participants were those who completed the 2-dose mRNA vaccine and had no previous polymerase chain reaction-confirmed COVID-19. Results show that of the 658 participants, 98 (15%) participants had an antibody response after 1 dose and after two doses, 357 had a response (54%). After receiving the first dose, 259 (39%) had no response, but once they received the second dose, they had a successful response. Although the humoral response increased after 2 doses, solid organ transplant recipients remain vulnerable to COVID-19 and additional research is needed to improve vaccine response for this population.