Varicella Vaccination for a 20-Year-Old
A healthy 20-year-old without evidence of varicella immunity should receive two 0.5-mL doses of single-antigen varicella vaccine administered subcutaneously, 4-8 weeks apart 1, 2, 1.
Vaccination Schedule
The ACIP guidelines are clear and consistent across multiple publications:
- Dose: Two 0.5-mL doses of single-antigen varicella vaccine
- Route: Subcutaneous administration
- Interval: 4-8 weeks between doses (minimum 4 weeks) 1
- Flexibility: If more than 8 weeks elapse after the first dose, the second dose may still be administered without restarting the schedule 1
Important Considerations Before Vaccination
Evidence of Immunity Assessment
Before vaccinating, determine if the patient already has evidence of immunity 2:
- Documentation of 2 doses of varicella vaccine at least 4 weeks apart
- Laboratory evidence of immunity or confirmed disease
- History of varicella or herpes zoster diagnosed or verified by a healthcare provider
- Note: Being U.S.-born before 1980 is NOT considered evidence of immunity for this 20-year-old (this criterion applies only to general adults, not healthcare personnel or pregnant women) 2
Vaccine Selection
- Use only single-antigen varicella vaccine for persons aged >13 years
- MMRV (combination vaccine) is NOT licensed for use in persons >13 years 1
Rationale for Two-Dose Schedule
The two-dose recommendation is critical because:
- Varicella disease is more severe and complications more frequent among adolescents and adults compared to children 1
- A single dose provides suboptimal protection, with breakthrough varicella occurring in approximately 4% of vaccinees annually 3
- Two doses provide approximately 85% protection against all forms of varicella and nearly 100% protection against severe forms 3
Special Priority Groups
While all adults without immunity should be vaccinated, special consideration should be given if the 20-year-old falls into high-risk categories 1:
- Healthcare personnel
- College students or those in postsecondary education
- Household contacts of immunocompromised persons
- Teachers or daycare employees
- Military personnel
- International travelers
- Nonpregnant women of childbearing age
College students face particularly high transmission risk due to high contact rates in institutional settings 1.
Common Pitfalls to Avoid
- Do not use MMRV vaccine in adults—this is only licensed for children 12 months to 12 years 1
- Do not accept birth before 1980 as evidence of immunity for this age group without additional verification 2
- Do not delay the second dose beyond 8 weeks unnecessarily, though it remains valid if given later 1
- Do not restart the series if the interval exceeds 8 weeks—simply give the second dose 1
Safety Profile
The vaccine is generally well-tolerated with:
- Mild injection site reactions and moderate fever being most common 3
- Varicella-like rash occurring rarely (not observed in some studies) 4
- No increased safety concerns with the two-dose schedule 5
Contraindications to Screen For
Since this is a live attenuated vaccine, proper evaluation for contraindications is essential 6:
- Pregnancy (contraindicated; vaccinate postpartum if needed)
- Severe immunocompromising conditions (HIV with CD4 <200 cells/μL, immunosuppressive therapy)
- Recent receipt of antibody-containing blood products (timing-dependent)