Reduced IgG antibody avidity in organ transplant recipients after varicella-zoster-virus vaccination

Objectives: The present study was designed to investigate the varicella-zoster-virus (VZV) IgG antibody avidity as a marker of memory priming and functional affinity of antibodies in pediatric solid organ transplant (SOT) recipients several years after pre-transplant VZV vaccination. Methods: The serum samples of SOT recipients were evaluated for IgG antibody levels against VZV and IgG antibody avidity. Twenty-eight patients were included in the study (20 had had liver transplantation, 3 heart transplantation, 5 kidney transplantation) and had received a single dose of Varivax (Aventis Pasteur, Lyon, France) prior to transplantation. The control group consisted of 50 healthy children, 36 of whom had had clinical and serological confirmed varicella infection after wild-virus contact and 14 of whom had varicella vaccination with a single dose of Varivax. Results: Median IgG antibody levels were 800 U/ml in wild-virus infected controls, 810 U/ml in vaccinated controls and 630 U/ml in SOT recipients. Median relative avidity index (RAI) was 89% for wild-virus infected controls, 94% for vaccinated controls and 82% for transplant recipients (p=0.01 compared to wild-virus infected controls, p=0.002 compared to vaccinated controls). Conclusions: IgG antibody avidity in SOT recipients may serve as an additional marker to evaluate humoral immunity against VZV. This is of particular importance in the clinical setting of exposure to VZV. However, the role of humoral protection against VZV has to be evaluated in long-term follow-up, since also cellular immunity may play a crucial role in defence against viral infections.