Varicella-Zoster Virus (VZV) IgG Antibody
VZV IgG antibody is a specific immunoglobulin that indicates past infection with or vaccination against varicella-zoster virus and provides long-term immunity against the virus. This antibody is crucial for determining immune status to VZV, which causes both chickenpox (varicella) and shingles (herpes zoster).
What VZV IgG Antibody Is
VZV IgG antibody is part of the body's adaptive immune response to varicella-zoster virus. When a person is exposed to VZV through either natural infection or vaccination, the immune system produces:
- IgM antibodies (short-term, acute response)
- IgG antibodies (long-term immunity)
The presence of VZV IgG antibodies in the blood indicates that a person has been previously exposed to the virus or has been vaccinated against it 1. These antibodies bind to various viral proteins and help protect against future infections or reactivations.
Clinical Significance
Determining Immunity Status
VZV IgG antibody testing is used to:
- Assess immunity status in individuals with unknown history of chickenpox
- Evaluate vaccine response
- Determine susceptibility to VZV in high-risk populations
High-Risk Populations Requiring VZV Immunity Assessment
- Pregnant women without known history of varicella 2
- Immunocompromised patients 2
- Healthcare workers
- Transplant recipients 3
Interpretation of Results
- Positive VZV IgG: Indicates immunity due to past infection or vaccination
- Negative VZV IgG: Indicates susceptibility to VZV infection
- Antibody avidity: The strength of antibody binding to antigens can be measured as relative avidity index (RAI) 3
It's important to note that solid organ transplant recipients may have lower antibody avidity despite having similar IgG concentrations compared to healthy controls 3. This suggests that quantitative antibody levels alone may not fully represent protective immunity in immunocompromised patients.
Clinical Applications
Post-Exposure Prophylaxis Decision-Making
VZV IgG antibody status helps determine the need for post-exposure prophylaxis with VariZIG (Varicella Zoster Immune Globulin) in exposed susceptible individuals 2.
The decision to administer VariZIG depends on three key factors:
- Whether the patient lacks evidence of immunity (negative VZV IgG)
- Whether the exposure is likely to result in infection
- Whether the patient is at greater risk for complications than the general population 2
Patient Groups for Whom VariZIG is Recommended (if VZV IgG Negative)
- Immunocompromised patients without evidence of immunity
- Newborn infants whose mothers develop varicella around delivery (5 days before to 2 days after)
- Hospitalized premature infants born at ≥28 weeks whose mothers lack immunity
- Hospitalized premature infants born at <28 weeks or weighing ≤1,000g regardless of maternal immunity
- Pregnant women without evidence of immunity 2
Testing Methods
Modern testing methods for VZV IgG antibodies include:
- Enzyme-linked immunosorbent assays (ELISAs): Laboratory-based method requiring serum or plasma
- Lateral flow immunochromatographic assays (LFAs): Point-of-care testing from fingerstick blood samples 4
Recent advancements have led to the development of rapid point-of-care tests that can detect VZV IgG antibodies from fingerstick blood samples within 20 minutes, offering higher sensitivity compared to traditional ELISA methods 4.
Clinical Pitfalls and Considerations
- Immunocompromised patients: May have reduced VZV-specific lymphocytes and lower antibody avidity despite having detectable IgG levels 3
- Bone marrow transplant recipients: Should be considered non-immune regardless of previous history of varicella or vaccination 2
- False negatives: Can occur in immunocompromised patients with impaired antibody production
- Cross-reactivity: Possible with other herpesvirus antibodies, though modern assays have improved specificity
Beyond Chickenpox: VZV and Stroke Risk
Recent research has identified VZV as a common cause of stroke in both children and adults. VZV vasculopathy can occur following zoster and is confirmed by the presence of either VZV DNA or anti-VZV IgG antibody in cerebrospinal fluid 5. This highlights the importance of understanding VZV immunity beyond its traditional association with chickenpox and shingles.