© 2022Objectives and aims: Disease modifying therapies used in multiple sclerosis can decrease humoral response after COVID-19 vaccines. This problem must be adequately addressed because new variants evolve, and COVID-19 still poses a risk to patients with comorbidities and immunosuppression. We aimed to evaluate the antibody response after the third dose of the COVID-19 vaccine in people with multiple sclerosis on disease-modifying therapies. Methods: People with multiple sclerosis who received the third dose of either mRNA or inactivated vaccine after two doses of inactivated vaccine were recruited for the study. Blood samples were collected at least two weeks after the third dose. Results: Blood samples of 339 (female 72.5%) people with multiple sclerosis and 52 (female 71.2%) healthy controls were evaluated. Healthy controls (mean: 4.07 ± 0.66) have higher antibody titers than people with multiple sclerosis (mean: 2.79 ± 2.95). Seronegative cases were observed only in the fingolimod and ocrelizumab treatment groups. Patients on fingolimod who received mRNA as a third dose had significantly higher antibody titer than those who had inactivated vaccines. Longer disease duration, having inactivated vaccine as a third dose, and DMT use was associated with lower antibody response. Conclusions: The study shows that even after inactivated vaccine schedule, mRNA still offers more protection in people with multiple sclerosis on disease-modifying therapies.