What is the recommended dose and schedule for varicella (chickenpox) vaccination in children and adults?

Varicella Vaccination Dosing

All children should receive two 0.5 mL subcutaneous doses of varicella vaccine: the first dose at 12-15 months of age and the second dose at 4-6 years of age, with a minimum 3-month interval between doses for children under 13 years, or a minimum 4-week interval for adolescents and adults 13 years and older. 1

Pediatric Dosing Schedule (12 months through 12 years)

• First dose: Administer at 12-15 months of age as a 0.5 mL subcutaneous injection 1
• Second dose: Administer at 4-6 years of age (before entering prekindergarten, kindergarten, or first grade) 1
• Minimum interval: 3 months between doses is the recommended minimum for this age group 1
• Acceptable early dosing: If the second dose is inadvertently given between 28 days and 3 months after the first dose, it does not need to be repeated 1

The strategic timing of the second dose at 4-6 years is based on CDC data showing higher varicella incidence and outbreak rates among elementary school-aged children compared to preschool-aged children 1. This two-dose schedule is now required for school entry in most states 1.

Adolescent and Adult Dosing (≥13 years)

• Two doses required: Administer two 0.5 mL subcutaneous doses 1
• Minimum interval: 4 weeks (28 days) between doses 1
• Vaccine formulation: Only single-antigen varicella vaccine (Varivax or Varilrix) may be used, as MMRV is not licensed for this age group 1

Available Vaccine Products

• Varivax (monovalent): Approved for ages ≥12 months, contains minimum 1,350 plaque-forming units per 0.5 mL dose 1
• Varilrix (monovalent): Approved for ages ≥12 months, 0.5 mL subcutaneous dose 2
• ProQuad (MMRV combination): Approved only for ages 12 months through 12 years 1

Critical safety note for ProQuad: For children aged 12-47 months receiving their first dose, the CDC recommends using separate MMR and varicella vaccines rather than ProQuad unless parents prefer MMRV after discussing the increased febrile seizure risk (approximately one additional febrile seizure per 2,300-2,600 doses in children aged 12-23 months) 3. ProQuad is preferred for children ≥48 months, as no increased febrile seizure risk exists in the 4-6 year age group 3.

Clinical Efficacy of Two-Dose Regimen

The two-dose schedule provides substantially superior protection compared to single-dose vaccination:

• Vaccine efficacy: 98% with two doses versus 94% with one dose 1
• Breakthrough disease prevention: Recipients of two doses are 3.3-fold less likely to develop breakthrough varicella 1
• Antibody response: >99% of children achieve protective antibody levels after two doses, compared to only 76-85% after a single dose 1, 4

Catch-Up Vaccination

• Never-vaccinated children aged 7 years: Administer two doses at least 3 months apart (minimum acceptable interval is 28 days) 1
• Previously received one dose: All children and adolescents who received only one dose should receive a second dose to complete the series 1
• No need to restart: Regardless of time elapsed since the first dose, simply continue with the second dose 1

Priority Populations for Adult Vaccination

Adults at increased risk who lack evidence of immunity require two-dose vaccination 1:

• Healthcare personnel
• Household contacts of immunocompromised persons
• Teachers and daycare employees
• College students and military personnel
• Nonpregnant women of childbearing age
• International travelers

Administration Timing with Other Live Vaccines

Critical timing rule: MMR and varicella vaccines must either be given on the same day OR separated by at least 28 days 3. Administering live virus vaccines less than 28 days apart (except simultaneously) may result in impaired immune response 3.

Contraindications

Varicella vaccine should NOT be administered to 1:

• Pregnant women
• Persons with severe anaphylactic reaction to neomycin or gelatin
• Persons with altered immunity (HIV with CD4 <15%, hematologic or solid tumors, congenital immunodeficiency)
• Persons on high-dose systemic corticosteroids (≥2 mg/kg/day prednisone or ≥20 mg/day for ≥14 days)
• Wait at least 1 month after discontinuing corticosteroid therapy before vaccinating 1

Common pitfall: Egg allergy is NOT a contraindication, as varicella vaccine contains no egg protein 1.

Storage and Handling

• Varilrix: Must be stored frozen at -15°C (5°F) or colder; use within 30 minutes after reconstitution 2
• Route: Subcutaneous administration is the only approved route 2