Background Some multiple sclerosis (MS) disease-modifying therapies (DMTs) impair responses to vaccines, emphasizing the importance of understanding COVID-19 vaccine immune responses in people with MS (PwMS) receiving different DMTs. Methods This prospective, open-label observational study enrolled 45 participants treated with natalizumab ( n  = 12), ocrelizumab ( n  = 16), fumarates (dimethyl fumarate or diroximel fumarate, n  = 11), or interferon beta ( n  = 6); ages 18–65 years inclusive; stable on DMT for at least 6 months. Responder rates, anti-SARS-CoV-2 spike receptor-binding domain IgG (anti-RBD) geometric mean titers (GMTs), antigen-specific T cells, and vaccination-related adverse events were evaluated at baseline and 8, 24, 36, and 48 weeks after first mRNA-1273 (Moderna) dose. Results At 8 weeks post vaccination, all natalizumab-, fumarate-, and interferon beta-treated participants generated detectable anti-RBD IgG titers, compared to only 25% of the ocrelizumab cohort. At 24 and 36 weeks post vaccination, natalizumab-, fumarate-, and interferon beta-treated participants continued to demonstrate detectable anti-RBD IgG titers, whereas participants receiving ocrelizumab did not. Anti-RBD GMTs decreased 81.5% between 8 and 24 weeks post vaccination for the non-ocrelizumab-treated participants, with no significant difference between groups. At 36 weeks post vaccination, ocrelizumab-treated participants had higher proportions of spike-specific T cells compared to other treatment groups. Vaccine-associated side effects were highest in the ocrelizumab arm for most symptoms. Conclusions These results suggest that humoral response to mRNA-1273 COVID-19 vaccine is preserved and similar in PwMS treated with natalizumab, fumarate, and interferon beta, but muted with ocrelizumab. All DMTs had preserved T cell response, including the ocrelizumab cohort, which also had a greater risk of vaccine-related side effects.