RESUMEN
Ocrelizumab is a novel humanized anti-CD20 antibody used for treatment of relapsing remitting and primary progressive multiple sclerosis with evidence of inflammatory activity. Guidelines suggest assessing vaccination status and eventually vaccinate patients with multiple sclerosis before new disease modifying therapy initiation. However, there are not any specific recommendations about vaccinal immunity reassessment after ocrelizumab injection. We describe the case of a patient who loss varicella zoster vaccinal immunity after the first ocrelizumab infusion. It is advisable to reassess vaccinal immunity to isolate non-immune patients and to adopt suitable preventive measures, including close contacts vaccination and avoidance of contacts with active infection.