Varicella-Zoster Virus IgG Significance
A positive varicella-zoster virus (VZV) IgG indicates immunity to VZV, either from prior natural infection (chickenpox) or from vaccination. This antibody persists long-term and serves as the primary marker for determining immune status and protection against future varicella infection 1.
Clinical Interpretation
VZV IgG-positive individuals are considered immune and protected against varicella, with the following key implications:
- Healthcare personnel (HCP) with positive VZV IgG do not require vaccination and are considered to have adequate evidence of immunity 1
- The antibody indicates past exposure through either natural chickenpox infection or successful vaccination 2, 3
- IgG antibodies persist for years to decades after initial infection or vaccination, with detection documented up to 11 years post-vaccination 1
Testing Methodology Considerations
The Advisory Committee on Immunization Practices (ACIP) provides specific guidance on VZV IgG testing:
- Latex agglutination (LA) and ELISA are the most widely used tests for detecting VZV IgG antibody after natural infection 1
- LA tests are generally more sensitive than commercial ELISAs and have sensitivity/specificity comparable to fluorescent antibody to membrane antigen (FAMA) testing 1
- For screening HCP for susceptibility, a less sensitive but more specific commercial ELISA should be considered to avoid false-positive results that could leave susceptible individuals unvaccinated 1
Important Testing Pitfall
LA tests can produce false-positive results, particularly when only a single serum concentration is evaluated, which has led to documented cases where HCP remained unvaccinated and subsequently contracted varicella 1. Recent data confirms that newer lateral flow assays demonstrate higher sensitivity (99.26%) compared to traditional ELISA (94.08%) 3.
Clinical Applications
VZV IgG testing serves multiple purposes in clinical practice:
- Immunity screening: Most commonly used in females aged 20-39 years (62-70% of testing) and represents the highest proportion of VZV testing (43-92% across data sources) 2
- Pre-employment screening: Essential for HCP to document immunity before patient contact 1
- Pregnancy planning: Identifies susceptible women who should receive vaccination before conception 2
- Post-vaccination confirmation: Can verify immune response after varicella vaccination, though antibody levels may be lower than after natural infection 4, 5
Distinction from Other VZV Antibodies
VZV IgG should not be confused with VZV IgM, which is not recommended for screening or routine diagnostic purposes despite comprising up to 11% of inappropriate testing in clinical practice 2. VZV IgM indicates acute or recent infection, while IgG indicates established immunity 6.
Special Populations
Bone marrow transplant recipients represent a unique exception: They should be considered non-immune regardless of previous varicella history or vaccination in themselves or their donors, unless they develop varicella or herpes zoster after transplantation 1.