Study design and populations.
The Japanese Pediatric Survey Holding Information of Nephrotic Syndrome (JP-SHINE) study, a nationwide cohort study, was established by the Japanese Study Group of Renal Disease in Children. The first survey was sent on 4 April 2014 to 1860 institutions throughout Japan, including all universities and children’s and general hospitals with more than 20 beds. Patients were eligible if they were newly diagnosed with idiopathic NS between 1 January 2010 and 31 December 2012, were between 6 months and 15 years old, and if they had been treated for up to 3 years during this time. Patients with congenital nephrotic syndrome or nephrotic syndrome secondary to nephritis were excluded. The first questionnaire, which was designed to record the number of children with idiopathic NS at each institution and their basic information, was sent to 1860 institutions. Of these, 1050 institutions (56.5%) responded to the first questionnaire20. The second questionnaire regarding patients who fulfilled the eligibility criteria was sent to 388 institutions and recorded information including patients’ basic characteristics, renal biopsy, idiopathic NS complications, steroid therapy side effects, and prognosis. We collected data for 999 patients21. In the present study, we recorded age when the patient received the first inactivated subunit-antigen flu vaccine, the total number of flu vaccinations received, total number of flu infections, total number of NS relapses, rituximab (RTX) use at the first flu vaccination, and immunosuppressant use at the first flu vaccination (cyclosporine, mycophenolate mofetil, mizoribine, cyclophosphamide, tacrolimus) between 1 May 2015 and 31 April 2016.
In the present study, the definitions of general conditions in pediatric NS were according to clinical guidelines issued by the Japanese Society for Pediatric Nephrology22,23. Idiopathic NS in children was defined as hypoalbuminemia (serum albumin levels ≤ 2.5 g/dL) and severe proteinuria (≥ 40 mg/h/m2 in pooled nighttime urine or an early morning urine protein creatinine (Cr) ratio > 2.0 g/g Cr). Complete remission was defined as a urine protein creatinine ratio < 0.2 g/g Cr or ≤ negative protein on early morning urine dipstick testing for 3 consecutive days. SSNS was defined as complete remission in < 4 weeks after starting daily prednisolone therapy. NS relapse was defined as ≥ 3 + protein on early morning urine dipstick testing for 3 consecutive days. FRNS was defined as two or more relapses within 6 months after initial response or four or more relapses within any consecutive 12-month period. SDNS was defined as two consecutive relapses occurring during steroid therapy or within 2 weeks of treatment cessation. SRNS was defined as the absence of complete remission after a 4-week course of oral prednisolone 60 mg/m2/day. RTX therapy duration was defined as the period from the day of rituximab administration to the day of B-cell recovery (CD19 + B-cell count ≥ 1% of total lymphocytes).
Influenza virus infection was diagnosed using rapid antigen detection tests with a nasopharyngeal swab sample or was clinically diagnosed by an attending pediatrician. In Japan, children younger than 13 years old generally receive flu vaccination twice per year and those over 13 years old are vaccinated once per year. In children who received two vaccinations in the same year, we defined the “first flu vaccine” as their first vaccination of the two. Antigen strains in inactivated flu vaccines between 2015 and 2016 were A/California/7/2009 (X-179A) (H1N1) pdm09, A/Switzerland/9715293/2013 NIB-88 (H3N2), B/Phuket/3073/2013, and B/Texas/2/2013.
Steroid therapy and immunosuppressants.
We adopted the modified International Study of Kidney Diseases in Children protocol, as shown in the Japanese pediatric idiopathic NS guideline2,23−25, and 63% of children were treated with the protocol, as follows. The initial 8-week treatment protocol was 60 mg/m2/day prednisolone (maximum daily dosage 60 mg) for 4 weeks, followed by 40 mg/m2/day (maximum daily dosage 40 mg) on alternate days for 4 weeks21.Thirty percent of children were treated with the prolonged protocol, which was initial treatment using a prolonged protocol of 60 mg/m2/day prednisolone (maximum daily dosage 60 mg) for 4 weeks, followed by 40 mg/m2/day (maximum daily dosage 40 mg) on alternate days, tapered over 2–6 months. Treatment in the remaining 7% of children was unknown. Immunosuppressants used between 1 May 2015 and 31 April 2016 were cyclosporine in 55%, mizoribine in 39%, cyclophosphamide in 13%, mycophenolate mofetil in 11%, RTX in 11%, and tacrolimus in 2% of patients.
This study was conducted according to the principles of the Declaration of Helsinki and following the ethical guidelines for Medical and Health Research Involving Human Subjects of the Ministry of Health, Labour and Welfare in Japan. Yokohama City University Hospital's central ethics review board approved this study (approval number: 1509001). This ethics committee clearly stated that the researchers did not need to obtain informed consent, because complete data in this study were collected from patient medical records. In accordance with this statement, informed consent was not required from patients or their parents in this study. According to the guidelines and the institutional ethics review board for the patients’ benefit, the protocol was displayed publicly in a poster at each hospital, and each patient or their family had the opportunity to refuse to be included in this analysis.
We used t-tests for continuous values and the chi-square and Fisher’s exact test for categorical values. All data were expressed as mean ± standard deviation or number (percentage). We used a MPRM for children who received or did not receive flu vaccination to calculate the risk ratio for flu infection, adjusted for receiving or not receiving flu vaccination, sex, age at NS onset, history of FRNS or SDNS or SRNS, flu infection in February or another month, and the risk ratio for NS relapse adjusted for whether the patients received flu vaccination, sex, age at NS onset, and history of FRNS or SDNS or SRNS. To evaluate the risk of NS relapse after flu vaccination, we used the MPRM only among children who received flu vaccination to calculate the risk ratio for NS relapse, adjusted for the post-vaccination period or pre-vaccination period, sex, and whether the patient was taking glucocorticoids or various immunosuppressants at flu vaccination. A P-value < 0.05 was considered statistically significant. We used SAS software package for Windows, release 9.4 (SAS Institute Inc. Cary, NC, USA) to perform all statistical analyses.
Data are available upon reasonable request.