lymphopenia/B-cell lymphopenia/T-cel lymphophenia/profound lymphopenia; hypogammaglobulinemia.; Worsening Diarrhea beginning one-week post rotavirus vaccination /unresolving diarrhea; electrolyte abnormalities; leukopenia; neutropenia; Stool rotavirus PCR was positive; This case was reported in a literature article and described the occurrence of lymphopenia in a 3-month-old female patient who received Rotavirus vaccine for prophylaxis. The patient's past medical history included full term baby. Additional patient notes included Ethnicity-, no pertinent family history.   On an unknown date, the patient received Rotavirus vaccine. On an unknown date, unknown after receiving Rotavirus vaccine, the patient experienced lymphopenia (serious criteria hospitalization), hypogammaglobulinemia (serious criteria hospitalization and GSK medically significant), diarrhea (serious criteria hospitalization), electrolyte abnormality (serious criteria hospitalization), leukopenia (serious criteria hospitalization and GSK medically significant), neutropenia (serious criteria hospitalization and GSK medically significant) and rotavirus test positive. The patient was treated with palivizumab, immunoglobulins nos (Ivig), sulfamethoxazole + trimethoprim (Bactrim) and fluconazole. On an unknown date, the outcome of the lymphopenia was recovering/resolving and the outcome of the hypogammaglobulinemia, electrolyte abnormality and rotavirus test positive were unknown and the outcome of the diarrhea, leukopenia and neutropenia were recovered/resolved.   The reporter considered the lymphopenia, hypogammaglobulinemia, diarrhea, electrolyte abnormality, leukopenia, neutropenia and rotavirus test positive to be related to Rotavirus vaccine.     Additional Information: GSK receipt date: 26 Jan 2023 Authors comment:  The patient was meeting age-appropriate milestones, had a negative newborn screen (NBS), including Severe combined immunodeficiency (SCID) screen, and no pertinent family history. The patient presented with worsening diarrhea beginning one-week post rotavirus vaccination. The patient was admitted for un-resolving diarrhea, electrolyte abnormalities, lymphopenia and hypogammaglobulinemia. Stool rotavirus PCR was positive 8 weeks after vaccination. Total immunoglobulin G (IgG) and Immunoglobulin M (IgM) were low. The presence of a thymus was confirmed on ultrasound. Esophagogastoduodenoscopy (EGD) and flexible sigmoidoscopy were grossly normal. The patient received palivizumab, Intravenous immune globulin (IVIG), and bactrim and fluconazole prophylaxis. Diarrhea resolved one week after hospitalization. Repeat NBS at 4 months of age demonstrated T-cell receptor excision circles (TRECs) of 28/ul. Absolute CD45RA and CD45RO were low. Adenosine deaminase (ADA) and Purine nucleoside phosphorylase (PNP) enzyme, whole exome genome sequencing, chromosomal microarray, and plasma amino acid profile were normal. At 8 months of age, the patient had mild B-cell lymphopenia with decreased absolute counts and normal percentage. The patient's leukopenia, neutropenia, and T-cell lymphopenia resolved. The temporal relationship of vaccine administration with onset of clinical findings, the persistently positive stool rotavirus PCR, and the absence of other clear etiology suggests rotavirus vaccine as the inciting factor for this patient's presentation. This case highlights a potentially rare subset of immunocompetent patients who could contract rotavirus infection from the rotavirus vaccine.