LAUSR

To the Editor: The varicella zoster virus (VZV) causes primary varicella infection (chickenpox), and reactivation of VZV causes herpes zoster (shingles). Varicella infection in children is usually mild but can be more severe in adults. Immunocompromised individuals are at risk for severe disease and have higher rates of complications. To prevent a potentially serious infection in immunosuppressed patients with inflammatory bowel disease (IBD), guidelines from American College of Gastroenterology recommend assessing varicella immunity in patients with IBD.1 Varicella infection has been vaccine-preventable since licensure of the live-attenuated varicella vaccine in 1995. The vaccine is a 2-dose series that is a part of the routine pediatric schedule in the United States.2 The presence of VZV antibodies indicates a previous varicella infection and protection against infection. VZV-specific antibody testing to assess immunity in those previously immunized with the varicella vaccine is not recommend by Advisory Committee on Immunization Practices and must be interpreted with caution. The varicella vaccine induces a 10-fold lower VZV antigen–antibody concentration compared with primary infection. The current commercial antibody, enzyme-linked immunosorbent assay (ELISA), is not sensitive enough to measure vaccine-induced VZV antibody levels in all patients, especially in those with a distant history of vaccination.2 Researchers from the Centers for Disease Control and Prevention found that their ELISA which is comparable with or more sensitive than commercial assays had a 34% false-negative rate when compared with the glycoprotein ELISA developed by Merck.3 A negative antibody test for varicella could be a false-negative result or waning of vaccine-induced protection over time. In those individuals whose antibody concentrations have waned over time and who have received 2 doses of varicella vaccine, cases of breakthrough varicella infection are rare.4 A false-negative varicella antibody has significant clinical implications in immunosuppressed patients with IBD. It could create undue anxiety of being at an increased risk for primary varicella infection. In addition, providers might withhold needed immunosuppressive therapy to immunize patients, and this could lead to IBD flares. Adult and pediatric gastroenterologist should be familiar with limitations of VZV serology using the commercially available assays when assessing varicella immunity in those immunized. We should consider relying more heavily on immunization history rather than current commercial ELISA to assess varicella immunity.