COVID-19 vaccination is highly recommended to multiple sclerosis (MS) patients. Little is known about the role of patients' clinical and demographic characteristics in determining antibody response.We evaluated safety and efficacy of anti-SARS-CoV-2 vaccines on 143 included MS patients. Then, we analyzed antibody titer in a subgroup, assessing clinical and demographic variables associated with protection and antibody titer.After completing the vaccination cycle, the rate of local adverse events was similar after the first and second dose. A higher proportion of systemic AEs was reported after the second dose (65.7% vs 24.5% after the first dose). Antibody response was evaluated in 97 patients. Higher EDSS (OR 0.6, 95% CI 0.4-0.9, p = 0.006) and treatment with antiCD20 (OR 0.02, 95% CI 0.003-0.098, p 0.001) were associated with a lower chance of having an efficacious response. Higher weight was associated with higher Ab titer (β = 15.2, 95% CI 2.8-27.6, p = 0.017), while treatment with antiCD20 with lower titers (β = - 1092.3, 95% CI - 1477.4 to - 702.2, p 0.001). In patients treated with antiCD20, hypogammaglobulinemia (β - 543, 95% CI - 1047.6 to - 39.1, p = 0.036) and treatment duration (β - 182, 95% CI - 341.4 to - 24.3, p = 0.027) were associated with lower Ab titer.Our study confirms that COVID-19 vaccination in MS patient is safe and effective in preventing symptomatic COVID-19 and should be recommended to all patients. Moreover, we suggest a possible role of hypogammaglobulinemia in reducing Ab response in patients treated with antiCD20 therapies.