received a third dose of the Pfizer/BioNTech vaccine six months after completing the initial series, however contracted a symptomatic non-complicated COVID-19 infection; COVID-19 infection; The initial case was missing the following minimum criteria: [No adverse effect]. Upon receipt of follow-up information on (26Apr2022), this case now contains all required information to be considered valid.  This is a literature report.  A 60-year-old female patient received BNT162b2 (BNT162B2), as dose 1, single (Batch/Lot number: unknown), as dose 2, single (Batch/Lot number: unknown) and as dose 3 (booster), single (Batch/Lot number: unknown) for covid-19 immunisation. The patient's relevant medical history included: "relapsing-remitting MS" (ongoing). Concomitant medication(s) included: OCRELIZUMAB taken for relapsing-remitting multiple sclerosis. The following information was reported: VACCINATION FAILURE (medically significant), outcome "recovered", described as "received a third dose of the Pfizer/BioNTech vaccine six months after completing the initial series, however contracted a symptomatic non-complicated COVID-19 infection"; COVID-19 (medically significant), outcome "recovered", described as "COVID-19 infection". The patient underwent the following laboratory tests and procedures: B-lymphocyte count: 0; Immunoglobulins: 744, notes: MG/DL; Lymphocyte count: 1.3; SARS-CoV-2 antibody test: without spike antibody response, notes: 30 days after the second dose of the series; positive, notes: two weeks after recovery from the natural infection and had seroconverted to positive antibody status; >10, notes: (INDEX VALUE). One patient on ocrelizumab received two doses of the Pfizer/BioNTech vaccine without spike antibody response 30 days after the second dose of the series. This patient received a third dose of the Pfizer/BioNTech vaccine six months after completing the initial series, however contracted a symptomatic non-complicated COVID-19 infection six weeks after the vaccine's third dose. Interestingly, this patient was tested for SARS-CoV2 spike protein antibody two weeks after recovery from the natural infection and had seroconverted to positive antibody status. Discussion: Although, B-cell therapy has been linked to reduced post-infectious and post-vaccination humoral response to SARS-CoV2, authors encountered one patient on ocrelizumab who initially tested negative for the spike protein antibody after completing two mRNA vaccine doses but eventually seroconverted after a third vaccine dose and a natural COVID19 infection. This suggests that repeated exposure to viral antigens may improve humoral responses in patients on B-cell therapy. It remains unclear whether booster or additional doses of vaccine will consistently lead to higher seroconversion rates among immunocompromised patients but this could be the set of future investigation.  The reporter considered "received a third dose of the pfizer/biontech vaccine six months after completing the initial series, however contracted a symptomatic non-complicated covid-19 infection" and "covid-19 infection" related to BNT162b2. No follow-up attempts are possible; information about lot/batch number cannot be obtained. No further information is expected.; Sender's Comments: Based on the information currently available, a lack of efficacy with bnt162b2 vaccine in this patient cannot be completely excluded