INTRODUCTIONSerological screening and vaccination play a crucial role in preventing infectious complications in patients with Multiple Sclerosis (MS). Standardization of tests and vaccination protocols are essential in patients undergoing treatment.OBJECTIVEThis study aimed to assess susceptibility to infectious diseases through serological tests and vaccine update of MS patients.METHODSA cross-sectional study was conducted on patients treated by the neurology service of the Metropolitan University of Santos between February 2021 and June 2023. Serological screening and vaccine recommendations were performed by an infectious disease specialist.RESULTSA total of 119 patients were included, with a mean age of 45.7 years. The sample was 68.1 % female and 31.9 % male, and vaccination update was performed for 64 (53.8 %) patients. MS treatments included: Glatiramer Acetate, Natalizumab, Fingolimod, Dimethyl Fumarate, Ocrelizumab and cladribine (Cladribine) and corticoid for MS flare-ups. Seroprevalence was: 66.0 % for the JC virus, 61.4 % Toxoplasmosis, 50.9 % Mononucleosis, 84.5 % Cytomegalovirus, 85.4 % Measles, 72.2 % Mumps, 92.6 % Rubella, and 94.2 % Varicella. No cases of HIV, HCV, HBV, HTLV or syphilis were detected. Vaccine cover was: 75 % influenza, 68.7 % Hepatitis B, 64.2 % Hepatitis A, 34.4 % HPV, 85 % COVID-19, 1.56 % Herpes Zoster, Diphtheria, Tetanus and Pertussis, 70 % DT, 6.5 % DTaP, 53 % anti-pneumococcal with Pn-23 and 31 % with Pn-13, 48.4 % Haemophilus influenzae b, 39 % Meningococcal C and 20.3 % ACWY.CONCLUSIONMS patients using immunosuppressant therapy may be susceptible to vaccine-preventable infectious diseases. The study demonstrates the feasibility of vaccine updates, and infectious diseases specialists can contribute assessing infection risks and providing individualized vaccines recommmendations.