Meaning of a Positive Varicella-Zoster Virus (VZV) IgG Antibody Result
A positive Varicella-Zoster Virus (VZV) IgG antibody result indicates immunity to VZV through either previous natural infection or vaccination, meaning the individual is protected against chickenpox and has a significantly reduced risk of developing the disease if exposed to the virus. 1
Interpretation of Positive VZV IgG Results
A positive VZV IgG antibody test is considered evidence of immunity to varicella (chickenpox) according to CDC guidelines 2, 1
This immunity may have been acquired through:
- Previous natural infection with varicella (chickenpox)
- Previous vaccination with the varicella vaccine
- Previous development of herpes zoster (shingles)
Individuals with positive VZV IgG antibody results:
- Are considered protected against future varicella infection
- Do not require vaccination
- Do not require Varicella Zoster Immune Globulin (VZIG) prophylaxis if exposed to someone with active varicella 2
Clinical Significance
- For healthcare workers: A positive VZV IgG result allows continued clinical duties even after exposure to varicella patients 1, 3
- For immunocompromised patients: A positive result indicates some level of protection, though the degree may vary depending on the severity of immunosuppression 2
- For bone marrow transplant recipients: These patients are considered an exception and should be considered non-immune regardless of previous history or antibody status until they develop varicella or herpes zoster after transplantation 2
Test Characteristics and Limitations
- Commercial ELISA tests for VZV IgG have high specificity but may have limited sensitivity, especially for vaccine-induced immunity 1
- 25-34% of vaccinated individuals with actual immunity may test negative on standard commercial ELISAs 1
- More sensitive tests like Fluorescent Antibody to Membrane Antigen (FAMA) or latex agglutination may detect antibodies in individuals who test negative by ELISA 1, 3
Special Considerations
- IgG antibody levels may wane over time but do not necessarily indicate loss of protection 1
- Cell-mediated immunity (CMI) also plays an important role in protection against VZV and may be present even with low or undetectable antibody levels 4
- In one study, 41.5% of individuals with intermediate IgG levels and 3.7% with negative IgG levels still had positive cell-mediated immunity 4
Post-Exposure Management
- Individuals with positive VZV IgG results who are exposed to varicella:
- Do not require post-exposure prophylaxis
- Can continue normal activities without restrictions
- Should be monitored for symptoms if immunocompromised, though risk is low 2
Important Caveats
- A positive IgG result does not indicate active infection - it only indicates past infection or vaccination
- For diagnosis of active chickenpox or shingles, direct detection methods from lesion samples are preferred 1
- IgG testing cannot distinguish between immunity from natural infection versus vaccination
- Positive IgG results may persist for decades after infection, with studies showing detectable antibodies more than 20 years after natural infection 5