Diagnosed with COVID-19 two months after completing the Pfizer vaccination course; Diagnosed with COVID-19 two months after completing the Pfizer vaccination course; INTRODUCTION: Vaccinations against Novel Coronavirus 2019 (COVID-19) for immunocompromised individuals have been increasingly prioritized to avoid severe infection. Here is a case of severe COVID-19 infection in a patient with malignant lymphoma who completed the vaccination course.CASE PRESENTATION: A 79-year-old male with malignant lymphoma on active Rituximab was diagnosed with COVID-19 two months after completing the Pfizer vaccination course. He presented with a worsening cough despite receiving monoclonal antibodies outpatient. On evaluation, his vitals were stable. Chest x-ray revealed bilateral pleural effusions with bibasilar opacities. During his hospitalization, he received a full course of dexamethasone, ivermectin, remdesivir and baricitinib. However, his cough and oxygenation progressively worsened, with eventual intubation and vasopressor support. Computed Tomography (CT) Chest showed progressive worsening of COVID-19 Pneumonia. Originally on admission he had tested negative for the IgM and IgG antibodies against the Nucleocapsid (N) Protein which raised the suspicion that he had not mounted an immune response to the vaccine. On further evaluation, he was found to have positive antibody titers against Spike (S) proteins which confirmed that he had mounted a response to the vaccine despite his imnmunocompromised status. DISCUSSION: Anti-CD20 therapy is one of the primary therapies for hematological malignancies. Despite T cell function being the primary role against COVID-19, there is increasing evidence that B-cell depletion may inhibit protective immunity following infection and vaccination. A two-dose regimen of BNT162b2 (Pfizer) conferred 95% protection against COVID-19 in persons 16 years of age or older, and decreased the rate of severe infection. However, only 4% of the vaccinated patients suffered from any malignancy; 0.2% of them had metastatic solid tumors, leukemia, lymphoma and none were on chemotherapy. The efficacy of the vaccine was extrapolated to include the subset of individuals on active chemotherapy. Interestingly, despite having an active immunological response to the vaccine and normal T-cell function, the patient suffered from severe COVID pneumonia. CONCLUSIONS: Though widespread immunization against COVID-19 is underway, patients with hematological malignancies still remain a vulnerable population. The decision to halt immunomodulatory therapy to improve efficacy of the vaccine needs further investigation.; Sender's Comments: Efficacy of the vaccine varies from patient to patient. However, a contributory role of the usage of the vaccine BNT162B2 to the reported events vaccination failure and COVID-19  (two months after completing the Pfizer vaccination course) cannot be excluded. The impact of this report on the benefit/risk profile of the Pfizer product is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to Regulatory Authorities, Ethics Committees and Investigators, as appropriate.