What does a varicella (chickenpox) titer of 24.8 indicate regarding immunity and need for vaccination?

Interpreting a Varicella Titer of 24.8

A varicella titer of 24.8 indicates adequate immunity against varicella (chickenpox) and no need for vaccination based on current guidelines and evidence.

Understanding Varicella Antibody Titers

Varicella antibody titers are used to assess immunity to the varicella-zoster virus (VZV). Different testing methods use different scales and reference ranges:

• gpELISA (glycoprotein enzyme-linked immunosorbent assay):

  • A titer of ≥5 gpELISA units/mL is associated with protection against disease 1
  • 86% of children achieve this level after one dose of vaccine 1

• FAMA (fluorescent antibody to membrane antigen):

  • A titer of >1:4 at 16 weeks post-vaccination correlates with protection 1
  • <1% of people with this titer develop varicella after household exposure 1

• Commercial ELISA tests:

  • Less sensitive than research assays but more specific than other commercial tests 2
  • Preferred for screening healthcare personnel 2

Interpretation of Your Result

Your titer of 24.8 is well above the protective threshold of 5 gpELISA units/mL (assuming the same or equivalent units). This indicates:

1. Strong immunity against varicella infection
2. No need for vaccination or additional doses
3. Long-term protection is likely, as antibody persistence has been demonstrated for up to 20 years in studies 1

Important Considerations

Limitations of Commercial Assays

Standard commercial assays may sometimes fail to detect vaccine-induced immunity despite actual protection:

• Commercial tests were originally designed to detect the higher antibody levels from natural infection 2, 3
• Approximately 25-34% of vaccinated individuals may test negative despite being protected 2
• More sensitive tests like FAMA or latex agglutination may be warranted in certain cases 3

Special Populations

For healthcare workers or immunocompromised patients:

• Healthcare workers should be screened for varicella immunity using IgG testing 2
• A titer of 24.8 would be considered protective in these populations
• Studies show that individuals with negative titers after vaccination can achieve positive status after an additional dose 4

Conclusion

Your varicella titer of 24.8 demonstrates robust immunity against varicella. No further vaccination is required, and you can be considered protected against chickenpox infection. This level of antibody is associated with a very low risk of breakthrough infection even upon exposure to the virus.