An adolescent girl diagnosed with IgA nephropathy following the first dose of the COVID-19 vaccine.

There has been growing interest in reported cases of IgA nephropathy (IgAN) flare-up following administration of the coronavirus disease 2019 (COVID-19) vaccine. Our patient is a previously healthy 17-year-old girl who presented with a 10-year history of microscopic hematuria. Because there were no abnormal findings in blood examination or ultrasonography, we followed her up twice per year as asymptomatic hematuria. Although she never developed gross hematuria when she had upper respiratory infections or received an influenza vaccine, she presented with gross hematuria and proteinuria within a few days after receiving the first dose of the Pfizer vaccine. We performed renal biopsy 2 weeks after the first vaccination. It revealed minor glomerular abnormalities with diffuse mesangial IgA deposits, and we diagnosed her with mild IgAN. Gross hematuria was detected after both the first and second doses, although it changed to microscopic hematuria within 1 week. Additionally, her proteinuria resolved spontaneously approximately 10 days after the second dose of the vaccine. Therefore, we opted to observe her without administering medication. The causation between COVID-19 vaccination and IgAN flare-up remains unclear. Several reports showed IgAN patients presenting gross hematuria following the second dose of the Pfizer or Moderna vaccines. However, our patient developed gross hematuria and proteinuria even after the first dose and without known severe acute respiratory syndrome coronavirus 2 exposure. Nephrologists should inform both patients with IgAN and those with asymptomatic hematuria that this side effect can occur even after the first vaccination.