Varicella Vaccine Dosing for a 27-Year-Old Adult
A healthy 27-year-old adult without documented chickenpox history or serologic immunity should receive two 0.5-mL doses of single-antigen varicella vaccine administered subcutaneously, with doses separated by 4-8 weeks (minimum interval of 4 weeks). 1, 2
Standard Two-Dose Regimen
- All adults aged 13 years and older without evidence of immunity require a two-dose series of varicella vaccine, with the second dose administered 4-8 weeks after the first dose 1, 2, 3
- The minimum acceptable interval between doses is 4 weeks, though waiting up to 8 weeks may result in higher antibody titers 1, 4
- Each dose is 0.5 mL administered subcutaneously 2, 3, 5
Evidence of Immunity (What Exempts Someone from Vaccination)
Your 27-year-old patient would need vaccination unless they have one of the following: 1, 2
- Documentation of 2 prior varicella vaccine doses at least 4 weeks apart
- Laboratory evidence of immunity or laboratory-confirmed disease
- Healthcare provider-diagnosed or verified history of varicella or herpes zoster
Note the critical exception: Being U.S.-born before 1980 does NOT count as evidence of immunity for healthcare personnel or pregnant women, but would apply to other adults 1, 2
Priority Considerations for This Age Group
- At age 27, this patient falls into several potential high-priority categories that warrant immediate vaccination if non-immune: healthcare workers, teachers, childcare employees, college students, military personnel, household contacts of children or immunocompromised persons, nonpregnant women of childbearing age, or international travelers 1, 2, 6
- Even without these risk factors, all non-immune adults should receive the vaccine 1
Contraindications to Screen For
Before administering the vaccine, verify the patient does NOT have: 6, 3
- Pregnancy (absolute contraindication; if female, ensure not pregnant and counsel to avoid pregnancy for 1 month after each dose) 6, 3
- Severe immunocompromising conditions including HIV with CD4 <200 cells/μL, active malignancy, or high-dose immunosuppressive therapy 1, 6, 3
- History of anaphylactic reaction to vaccine components 6, 3
Special Clinical Considerations
- Avoid salicylates for 6 weeks after vaccination due to theoretical Reye syndrome risk 3
- If other live vaccines are needed, administer on the same day or separate by at least 28 days 6, 3
- Recent immune globulin or blood product administration may interfere with vaccine response; consult ACIP spacing guidelines 3
- Tuberculin skin testing should be performed before vaccination, on the same day, or delayed at least 4 weeks after vaccination 3
Expected Efficacy
- The two-dose regimen provides 98% efficacy against any varicella disease and 100% efficacy against severe disease 2
- Seroconversion rates after two doses approach 99% in adolescents and adults 4
- Single-dose effectiveness is only 84.5% (median), which is insufficient for optimal protection 7
Common Pitfalls to Avoid
- Do not accept patient-reported history of chickenpox alone as evidence of immunity without healthcare provider verification or serologic confirmation 1
- Do not delay the second dose beyond 8 weeks unnecessarily, as this may reduce compliance and leave the patient vulnerable 8
- Do not administer during pregnancy or within 1 month of planned conception 3
- For cost-conscious settings, serologic testing before vaccination may be cost-effective in adults aged 20-29 years (71% are already immune), but only if compliance with follow-up vaccination is ≥75% 8