What does an elevated varicella (chickenpox) Immunoglobulin G (IgG) level indicate?

Interpretation of Elevated Varicella IgG Levels

An elevated varicella (chickenpox) IgG level indicates immunity to varicella-zoster virus (VZV), either from previous natural infection or vaccination. This immunity generally provides protection against developing chickenpox disease 1.

What Varicella IgG Positivity Means

• Positive varicella IgG antibodies in serum indicate immunity to varicella and protection from chickenpox disease 2
• Both healthy and immunocompromised individuals with verified positive varicella IgG may be considered immune (with the exception of bone marrow transplant recipients) 1
• The presence of varicella IgG antibodies serves as evidence of immunity, which can be acquired through:
  • Natural infection (having had chickenpox in the past)
  • Vaccination with the varicella vaccine
  • Maternal transfer (in newborns) 3

Differences Between Natural Immunity and Vaccine-Induced Immunity

• Natural infection typically produces higher antibody levels compared to vaccination, though both provide clinical protection 4, 5
• Despite similar antibody titers, individuals with natural chickenpox infection demonstrate significantly higher levels of VZV antigen-specific CD4 T cells compared to vaccinated individuals 5
• The IgG subclass response patterns differ slightly between natural infection and vaccination:
  • After natural infection, IgG1 antibodies appear within 2 weeks and persist for at least 10 years
  • IgG3 antibodies peak early but decline over time
  • IgG4 antibodies appear later (around 1 month) and persist long-term 6

Clinical Implications

• A positive varicella IgG test eliminates the need for varicella vaccination in most individuals 1
• Varicella-zoster immune globulin (VZIG) is not indicated for persons with documented immunity (positive varicella IgG) who are exposed to varicella 1
• For immunocompromised patients, the interpretation may differ:
  • Bone marrow transplant recipients should be considered non-immune regardless of previous history or positive antibody status 1
  • Patients who received 2 doses of varicella vaccine before becoming immunocompromised are generally considered protected 1

Limitations of Varicella IgG Testing

• Serologic tests for VZV antibodies vary in sensitivity and specificity 2
• A negative antibody test in previously vaccinated individuals does not necessarily indicate susceptibility due to the low sensitivity of some tests to detect vaccine-induced antibodies 1
• The CDC does not recommend serologic testing before or after immunization for varicella due to these limitations 1

Special Considerations

• Breakthrough varicella can occur in vaccinated individuals despite positive antibody status, though it is typically milder than disease in unvaccinated individuals 1
• In pregnant women, positive varicella IgG indicates protection against congenital varicella syndrome if exposed during pregnancy 3
• Varicella IgG antibodies are transferred across the placenta, providing temporary protection to newborns of immune mothers 3

Remember that while antibody testing is useful for determining immunity status, both antibodies and cellular immunity likely interact to provide complete protection against varicella-zoster virus 2.