IL6 and congenital rubella syndrome: Although the grade 4–5 infection and grade 3–5 CRS groups had much higher serum IL-6 compared to grade 1–3 infection and grade 1–2 CRS groups, only grade 3–5 CRS had significant concurrent elevation of ferritin (Additional file 1: Figure S3), which was not observed in grade 4–5 infection group.