Should a varicella (chickenpox) booster be given to a patient with a low varicella titer?

Should a Varicella Booster Be Given to a Patient with a Titer of 0.06?

Yes, administer a varicella booster to this patient, as a titer of 0.06 is below the protective threshold and indicates lack of adequate immunity.

Understanding the Titer Result

• A varicella titer of 0.06 is significantly below the protective threshold of ≥0.3 gpELISA units that defines seroconversion and immunity 1
• Commercial ELISA tests may be less sensitive than other assays like FAMA or latex agglutination, but a titer this low (0.06) indicates clear seronegativity regardless of assay type 2, 3
• Patients with titers <5 gpELISA units are 3.5 times more likely to develop breakthrough varicella compared to those with titers >5 units 1

Vaccination Recommendation Based on Immune Status

For patients aged ≥13 years:

• Administer 2 doses of single-antigen varicella vaccine separated by 4-8 weeks 1, 2
• This patient requires the full 2-dose series as they lack evidence of immunity 1

For children aged 1-12 years:

• Administer 2 doses separated by ≥3 months 1
• The second dose provides significantly improved immunologic response with 99.6% achieving protective titers (>5 gpELISA units) compared to 85.7% after one dose 1

Critical Considerations Before Vaccination

Assess immunocompetence status first:

• If immunocompetent: Proceed with standard 2-dose vaccination schedule 1
• If on or planning immunosuppressive therapy: Vaccinate ≥4 weeks before starting therapy when possible 1
• If highly immunocompromised: Varicella vaccine is contraindicated due to risk of severe vaccine-strain disease 1
• If receiving low-level immunosuppression: Vaccination can be considered on a case-by-case basis 1

Post-Vaccination Monitoring

• Seroconversion occurs in approximately 97% of susceptible children and 79% of adolescents after one dose, with higher rates after two doses 1
• Do not routinely recheck titers after documented 2-dose vaccination, as documented receipt supersedes subsequent serologic testing 2
• However, if retesting is performed and remains negative, consider a third dose, which has shown 100% seroconversion rates in initial non-responders 4, 5

Common Pitfalls to Avoid

• Do not assume this patient is protected - a titer of 0.06 is clearly non-protective and requires vaccination 1, 2
• Do not use combination MMRV vaccine in immunocompromised patients - use single-antigen varicella vaccine only 1
• Do not delay vaccination in healthcare workers or household contacts of immunocompromised persons, as these are priority groups 2
• For women of childbearing age: Counsel to avoid conception for 1 month after each vaccine dose 1

Special Population Considerations

Healthcare personnel:

• This low titer mandates vaccination to prevent nosocomial transmission 2, 6
• Even after 2 doses, approximately 12% of vaccinated healthcare workers remain seronegative and require additional doses 6

HIV-infected patients:

• Can receive vaccine if CD4+ T-lymphocyte count >200 cells/µL (adults) or CD4+ percentage >15% (children), using 2 doses separated by 3 months 1