A 28 years old lady with history of microscopic haematuria for 5 years underwent a pre-scheduled kidney biopsy for suspected IgA nephropathy. Her renal function was normal with proteinuria 0.11 g/day. 3 weeks prior to biopsy, she received her second dose of mRNA COVID-19 vaccine (Pfizer-BioNTech BNT162b2) and developed painless gross hematuria 3 h later. Serum creatinine level was mildly elevated from 58 to 72 μmol/L. Urine protein creatinine ratio increased from 20 to 320 mg/mmol. Her anti-nuclear antibody (ANA) turned from negative to positive with a titre of 1: 640, but anti-dsDNA remained negative. Her C3 and C4 levels were normal. 5 days later, her serum creatinine level fell to 54 μmol/L and hematuria subsided spontaneously. 3 weeks later, her urine protein creatinine ratio fell to 34 mg/mmol and ANA became negative. Kidney biopsy confirmed IgA nephropathy with Oxford classification M1E0S0T0-C0 without features suggestive of lupus nephritis.

The second patient was a 58 years old lady with hypertension and microscopic haematuria for 1 year. She recalled an episode of painless gross haematuria in 2008. CT urogram and cystoscopy were normal. There were 4% dysmorphic red blood cells in urine. Urine protein creatinine ratio was 24 mg/mmol. IgA nephropathy was suspected clinically. Kidney biopsy was not arranged. 1 day after her second dose of Pfizer-BioNTech mRNA COVID-19 vaccine, she developed painless gross haematuria lasting for 2 days. Her serum creatinine level remained stable at 78 μmol/L 3 weeks later.

To date, at least 15 cases of acute flare of IgA nephropathy after COVID-19 vaccination have been published, involving both the Pfizer-BioNTech and Moderna mRNA vaccines. All of them had gross haematuria, mostly within 6 to 24 h after the second dose vaccination, with or without increase in proteinuria. Most of them had spontaneous resolution after a few days. Only two patients required steroid therapy for acute kidney injury.1, 2 Our first patient had earliest onset of gross haematuria within just 3 h. The transient strongly positive ANA indicates that the COVID-19 vaccination may trigger more generalized immunological response beyond just stimulating IgA production. Reactivation of and new onset lupus nephritis after COVID-19 vaccination with elevated ANA titre have also been reported recently, one after mRNA and the other after the AstraZeneca COVID-19 vaccination.3, 4 Flare of other glomerulonephritis has also been reported after different types of COVID-19 vaccination.5 Our second patient reflects that gross haematuria developing shortly after COVID-19 vaccination may reflect or unmask the presence of pre-existing IgA nephropathy. As flare of IgA nephropathy after COVID-19 vaccination is uncommon and mostly benign, it should not be a reason for deterring vaccination. More data on the incidence and significance of acute flare of IgA nephropathy after COVID-19 vaccination will be very useful.