To the editor:

We read with great interest the report of Negrea and Rovin of 2 cases of IgA nephropathy with gross hematuria following the Moderna vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).¹ We also cared for a 52-year-old Asian female with prior biopsy-proven IgA nephropathy who developed gross hematuria within 24 hours of receiving a second dose of the Pfizer vaccine. Table 1 summarizes clinical data. Her workup was notable for proteinuria of 4.2 g/g of creatinine with serum creatinine at baseline. Of note, SARS-CoV-2 antibody testing prior to vaccination was negative, and she developed no symptoms after the first vaccine dose. Repeated testing within 1 week demonstrated resolution of hematuria and improving proteinuria. Interestingly, she developed gross hematuria following the first shot of the Shingrix vaccine 2 years prior but no symptoms following annual influenza vaccinations. The IgA nephropathy flare in our patient following the second SARS-CoV-2 vaccine dose without known prior exposure to SARS-CoV-2 suggests it was mediated by a delayed-type hypersensitivity reaction. Vasculitis flare-ups following vaccinations have been reported in the past.^{2 , 3}

Table 1

Patient symptoms and details of workup

Patient characteristic	Data
Year of IgAN diagnosis	2017
Exacerbations since diagnosis	1. April 2019 following URI 2. June 2019 following shingles vaccine
Current treatment	Lisinopril
Baseline Cre	0.7–0.8 g/dl
Last urine microalbumin/Cre before exacerbation (2020)	633.1 mg/g Baseline always <1000 mg/g, except exacerbations
Urine microalbumin/Cre 48 h after Pfizer second dose	2411.3 mg/g
Gross hematuria/RBCs in urine	Yes/yes
Other symptoms	Fever, myalgias, body aches, lower back pain bilaterally
Urine microalbumin/Cre 5 d after Pfizer second dose	1441 mg/g
Hematuria 5 d after Pfizer second dose	Resolved

Cre, creatinine; IgAN, IgA nephropathy; RBC, red blood cell; URI, upper respiratory tract infection.

Our patient’s symptoms improved within a week without any intervention aside from continued renin-angiotensin-aldosterone system blockade. It has been reported that severe coronavirus disease 2019 (COVID-19) illnesses can trigger an IgA response in the bronchial mucosa.⁴ However, it is unclear how a nonmucosal vaccine triggers this response. We suggest that nephrologists closely follow their patients after COVID-19 vaccination to evaluate for varying degrees of flares, particularly after the second dose of an mRNA vaccine without prior exposure to SARS-CoV-2.