What does a varicella (chickenpox) non-reactive result with a titer less than 1:135 indicate?

Interpretation of Varicella Non-Reactive Titer <1:135

A varicella (chickenpox) non-reactive result with a titer less than 1:135 indicates lack of immunity to varicella-zoster virus (VZV), meaning the individual is susceptible to chickenpox infection and requires vaccination. 1

Understanding Varicella Immunity Thresholds

Different laboratory methods measure varicella immunity with varying thresholds:

• FAMA test (gold standard): A titer of >1:4 at 16 weeks post-vaccination correlates with protection against disease 1

  • <1% of people with a titer >1:4 develop varicella after household exposure
  • 55% attack rate among those with titers <1:4

• gpELISA test:

  • ≥5 gpELISA units/mL indicates protection (95.5% vaccine efficacy) 1
  • <5 gpELISA units/mL indicates lower protection (83.5% vaccine efficacy) 1

• Commercial tests:

  • Commercial ELISA and latex agglutination tests are less sensitive than research assays 1
  • Commercial tests may not reliably detect vaccine-induced immunity, which produces lower antibody levels than natural infection 2

Clinical Implications of Non-Reactive Titer <1:135

A non-reactive titer <1:135 has important implications:

1. Susceptibility to infection: The individual lacks protective antibodies against varicella and is at risk for chickenpox if exposed 1

2. Vaccination recommendation:

   • For children: Two doses of varicella vaccine are recommended 1
   • For adolescents/adults: Two doses administered 4-8 weeks apart are recommended 1

3. Healthcare worker considerations:

   • Healthcare workers with non-reactive titers should not care for high-risk patients until vaccinated 2
   • Follow-up titers should be obtained after vaccination to confirm seroconversion 2

Potential Pitfalls in Interpreting Varicella Titers

Several important caveats should be considered:

• Test sensitivity limitations: Commercial ELISA tests may miss low-level immunity from vaccination 2

  • Some individuals may have adequate cell-mediated immunity despite low antibody titers 2
  • More sensitive tests (FAMA, latex agglutination) may detect antibodies missed by standard ELISA 2

• Vaccine vs. natural immunity: Vaccine-induced immunity typically produces lower antibody titers than natural infection 1

  • Commercial tests are designed to detect the higher titers from natural infection 2

• Immunocompromised status: Interpretation may differ in immunocompromised individuals who may not mount adequate responses to vaccination 1

Management Recommendations

For individuals with non-reactive varicella titers <1:135:

1. Immunocompetent individuals:

   • Administer 2 doses of varicella vaccine 4-8 weeks apart (adults/adolescents) or according to childhood schedule 1
   • Consider post-vaccination titer to confirm seroconversion, especially in healthcare workers 2

2. Healthcare workers:

   • Vaccinate and restrict from caring for high-risk patients until immunity is confirmed 2
   • If still non-reactive after two doses, consider more sensitive testing methods like FAMA 2

3. Post-exposure management:

   • For high-risk exposures in susceptible individuals, consider varicella-zoster immune globulin within 96 hours of exposure 3

Remember that some individuals may have cell-mediated immunity despite low antibody titers, which can provide protection against severe disease even with low or undetectable antibody levels 2.