What is the recommended varicella (chicken pox) vaccine schedule for children and adults?

Varicella (Chickenpox) Vaccine Schedule

All children should receive two 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 interval of 3 months between doses for children under 13 years. 1

Children (12 months through 12 years)

Primary Schedule

• First dose: Administer at 12-15 months of age 2, 1
• Second dose: Administer at 4-6 years of age (before entering prekindergarten, kindergarten, or first grade) 2, 1
• Minimum interval between doses: 3 months for children 12 months through 12 years 2, 1

Important Timing Considerations

• The second dose may be administered earlier than 4-6 years, provided the minimum 3-month interval is maintained 1
• 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 4-6 year timing is strategically chosen because varicella incidence and outbreaks are higher among elementary school-aged children 1

Catch-Up Vaccination

• Children who have never received varicella vaccine should begin the two-dose series immediately, with doses separated by at least 3 months 1
• All children entering school must have received two doses of varicella vaccine or have other evidence of immunity 1

Adolescents and Adults (≥13 years)

Primary Schedule

• Two doses required: Administer 0.5 mL doses separated by a minimum of 4 weeks (28 days) 2, 1
• Only single-antigen varicella vaccine (Varivax) may be used in persons ≥13 years, as MMRV is not licensed for this age group 1

Priority Populations for Vaccination

Adults at increased risk who lack evidence of immunity should receive special consideration for two-dose vaccination, including: 1

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

Vaccine Formulations and Administration

Available Products

• Monovalent varicella vaccine (Varivax): Approved for ages ≥12 months, contains minimum 1,350 plaque-forming units per 0.5 mL dose 1
• Combination MMRV vaccine (ProQuad): Approved only for ages 12 months through 12 years 1

Route and Dose

• Each dose is 0.5 mL administered subcutaneously 1

MMRV Vaccine Safety Considerations

• For first dose in children 12-47 months: Use separate MMR and varicella vaccines rather than MMRV unless parents express preference after discussing risks 1
• MMRV carries approximately one additional febrile seizure per 2,300-2,600 doses compared to separate vaccines in children aged 12-23 months 1
• For children ≥48 months: MMRV is preferred, as no increased febrile seizure risk has been demonstrated in children aged 4-6 years 1
• Personal or family history of seizures is a precaution for MMRV; use separate vaccines instead 1

Clinical Efficacy of Two-Dose Schedule

The two-dose regimen provides superior protection compared to single-dose vaccination: 1

• 98% efficacy against any varicella disease (vs. 94% with one dose)
• 100% efficacy against severe disease
• Recipients of two doses are 3.3-fold less likely to experience breakthrough varicella
• >99% of children achieve protective antibody levels after two doses (vs. 76-85% after one dose)

Contraindications

Absolute contraindications include: 1

• Severe anaphylactic reaction to vaccine components (neomycin or gelatin)
• Pregnancy
• Known altered immunity (HIV with CD4 <15%, hematologic or solid tumors, congenital immunodeficiency)
• 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 Misconceptions (NOT Contraindications)

• Egg allergy is NOT a contraindication (vaccine contains no egg protein) 1
• Contact dermatitis to neomycin is NOT a contraindication 1
• Having a pregnant household member is NOT a contraindication for vaccinating other family members 1

Special Populations

HIV-Infected Children

• May receive varicella vaccine if CD4 T-lymphocyte percentage ≥15% 1
• Use 2 doses of monovalent vaccine with a 3-month interval 1

Postexposure Prophylaxis

• Unvaccinated persons exposed to varicella should receive vaccine within 3 days of exposure (up to 5 days may provide some benefit) 1
• Vaccination within 3 days is >90% effective in preventing varicella 1
• Vaccination within 5 days is approximately 70% effective in preventing varicella and 100% effective in modifying severe disease 1

Critical Timing with Other Live Vaccines

MMR and varicella vaccines must be given either on the same day OR separated by at least 28 days 3

• Live virus vaccines given parenterally may interfere with each other's immune response if administered less than 28 days apart 3
• When given simultaneously, immune responses are identical to vaccines administered a month apart 3
• This prevents suboptimal immune response that can occur when live vaccines are given 1-27 days apart 3

Additional Precautions

• Avoid salicylates for 6 weeks after vaccination due to risk of Reye syndrome 1
• There is no need to restart a vaccine series regardless of time elapsed between doses 2