What is the recommended varicella (chickenpox) vaccine schedule for pediatric patients?

Varicella Vaccine Schedule for Pediatric Patients

All healthy 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 (before entering kindergarten or first grade). 1, 2

Standard Two-Dose Schedule

First Dose Timing

• Administer the first dose routinely at 12-15 months of age 1, 2, 3
• The vaccine is FDA-approved starting at 12 months of age 2
• This timing aligns with other routine childhood immunizations 3

Second Dose Timing

• Administer the second dose routinely at 4-6 years of age (before entering prekindergarten, kindergarten, or first grade) 1, 2, 3
• This timing is strategically chosen because varicella incidence and outbreaks are higher among elementary school-aged children compared to preschool-aged children 2
• The second dose may be given earlier than 4-6 years if needed, as long as the minimum interval is met 2

Minimum Intervals Between Doses

Children 12 Months Through 12 Years

• Minimum interval: 3 months between first and second doses 1, 2, 3
• If the second dose is inadvertently administered between 28 days and 3 months after the first dose, the second dose does not need to be repeated 1, 2
• The 3-month interval is based on clinical trial design that demonstrated optimal immunogenicity 2

Adolescents and Adults (≥13 Years)

• Minimum interval: 28 days (4 weeks) between doses 1, 2, 3
• Both doses should be 0.5 mL administered subcutaneously 1, 3

Vaccine Formulations Available

For Children 12 Months Through 12 Years

• Monovalent varicella vaccine (Varivax): Approved for ages ≥12 months 1, 2
• Combination MMRV vaccine (ProQuad): Approved only for ages 12 months through 12 years 1, 2
• Combination vaccines are preferred when all components are indicated to minimize injections 1

For Adolescents and Adults (≥13 Years)

• Only single-antigen varicella vaccine (Varivax) may be used 2
• MMRV is not approved for this age group 1, 2

Catch-Up Vaccination

Previously Unvaccinated Children

• Begin the two-dose series immediately at any age ≥12 months 2, 3
• No need to restart the series regardless of time elapsed 2
• For children aged 12 months through 12 years: give two doses separated by at least 3 months 1, 2

Children Who Received Only One Dose

• Administer the second dose to complete the series 1
• Follow the same minimum interval guidelines based on age 2

Rationale for Two-Dose Schedule

The two-dose recommendation is based on compelling efficacy data:

• Vaccine efficacy: 98% with two doses vs. 94% with one dose over a 10-year period 1, 2
• Recipients of two doses are 3.3-fold less likely to experience breakthrough varicella compared to one-dose recipients 1, 2, 3
• After two doses, >99% of children achieve protective antibody levels (≥5 U/mL by glycoprotein ELISA) 1, 2, 3
• Two doses provide 100% efficacy for prevention of severe disease 1

Administration with Other Vaccines

Simultaneous Administration

• Varicella vaccine can be safely administered simultaneously with other routine childhood vaccines without compromising immunogenicity 3
• When given on the same day, MMR and varicella vaccines produce immune responses identical to vaccines administered a month apart 4

Spacing with Live Vaccines

• Critical rule: MMR and varicella vaccines must either be given on the same day OR separated by at least 28 days 4
• Live virus vaccines given parenterally less than 28 days apart (except on the same day) may result in impaired immune response 4
• This is a common pitfall to avoid—never administer these vaccines 1-27 days apart 4

School Entry Requirements

• All children entering school should have received two doses of varicella vaccine or have other evidence of immunity 2
• As of 2012,36 states had implemented two-dose varicella vaccination elementary school entry requirements 5
• Two-dose coverage among 7-year-olds increased from 3.6%-8.9% in 2006 to 79.9%-92.0% in 2012 in sentinel sites 5

Common Pitfalls to Avoid

• Do not administer live vaccines 1-27 days apart: This may result in suboptimal immune response; either give them on the same day or wait at least 28 days 4
• Do not repeat the second dose if inadvertently given between 28 days and 3 months in children 12 months through 12 years 1, 2
• Do not use MMRV vaccine in adolescents or adults ≥13 years—only monovalent varicella vaccine is approved 2
• Do not delay vaccination unnecessarily, as this increases disease exposure risk during the unprotected interval 4