What are the recommendations for administering a Varicella (chickenpox) booster vaccine to a patient with a healthy immune system?

Varicella Booster Vaccination for Immunocompetent Patients

All healthy individuals who have received one dose of varicella vaccine should receive a second dose to complete the two-dose series, with timing based on age: children aged 1-12 years should receive the second dose at 4-6 years (minimum 3 months after first dose), while adolescents and adults ≥13 years should receive it 4-8 weeks after the first dose. 1, 2

Two-Dose Schedule: The Standard of Care

The two-dose varicella vaccination schedule is now the established standard for all immunocompetent individuals, replacing the previous one-dose recommendation. This change was driven by compelling evidence of superior protection and the inability of single-dose vaccination to prevent outbreaks even in highly vaccinated populations. 1, 3

Evidence Supporting Two Doses

• Vaccine efficacy increases from 94% with one dose to 98% with two doses, representing a clinically meaningful improvement in protection against any varicella disease 4, 5
• Recipients of two doses are 3.3-fold less likely to develop breakthrough varicella compared to one-dose recipients 1, 2, 3
• After two doses, >99% of children achieve protective antibody levels (≥5 gpELISA units), compared to only 76-85% after a single dose 1, 2
• Two-dose vaccination provides 100% efficacy against severe varicella disease 2

Age-Specific Dosing Recommendations

Children 12 Months Through 12 Years

• First dose: Administer at 12-15 months of age 1, 2
• Second dose: Routinely given at 4-6 years (before school entry), but may be administered earlier if at least 3 months have elapsed since the first dose 1, 2
• Minimum interval: 3 months between doses (though doses given 28 days to 3 months apart do not need repeating) 1, 2, 6

Adolescents and Adults ≥13 Years

• Two 0.5 mL doses of single-antigen varicella vaccine administered subcutaneously 1, 2
• Minimum interval: 4-8 weeks between doses (minimum acceptable is 4 weeks) 1, 2
• MMRV combination vaccine is NOT licensed for this age group—only single-antigen Varivax may be used 1, 2

Catch-Up Vaccination

All individuals who previously received only one dose of varicella vaccine should receive a second dose as catch-up vaccination, regardless of time elapsed since the first dose. 1, 2 The schedule does not need to be restarted—simply administer the second dose using the age-appropriate minimum interval. 2

Priority Populations for Catch-Up

Adults at increased risk who lack complete two-dose vaccination should receive special priority, 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 Product Selection

Available Formulations

• Varivax (single-antigen): Approved for all ages ≥12 months; contains minimum 1,350 PFU per 0.5 mL dose 2
• ProQuad (MMRV combination): Approved ONLY for children 12 months through 12 years 1, 2

Critical Safety Consideration for ProQuad

For the first dose in children aged 12-47 months, use separate MMR and varicella vaccines rather than ProQuad unless parents specifically prefer MMRV after discussing risks. 2 ProQuad carries approximately one additional febrile seizure per 2,300-2,600 doses in this age group compared to separate vaccines. 2

However, ProQuad is preferred for children ≥48 months (4-6 years), as post-licensure studies showed no increased febrile seizure risk at this age. 2

Timing Considerations with Other Live Vaccines

If MMR and varicella vaccines are not given on the same day, they must be separated by at least 28 days. 6 This is a critical principle: live virus vaccines given parenterally may interfere with each other's immune response if administered less than 28 days apart (unless given simultaneously). 6

Common Pitfall to Avoid

Do not administer varicella vaccine 1-27 days after MMR (or vice versa), as this may result in suboptimal immune response. Either give them together at the same visit or wait the full 28 days. 6

School Entry Requirements

All children entering school must have received two doses of varicella vaccine or have other evidence of immunity (prior disease, laboratory confirmation, or serologic evidence). 1, 2 The high transmission risk in school settings—where outbreaks continue to occur even with 96-99% one-dose vaccination coverage—necessitates this requirement. 3

Contraindications for Immunocompetent Patients

Varicella vaccine should NOT be given to: 1, 2

• Pregnant women (nonpregnant women should avoid pregnancy for 1 month after each dose)
• Persons with history of anaphylactic reaction to neomycin or gelatin
• Persons on high-dose systemic corticosteroids (≥2 mg/kg/day or ≥20 mg/day prednisone for ≥14 days)—wait at least 1 month after discontinuing before vaccinating

Important Clarifications

• Egg allergy is NOT a contraindication—varicella vaccine contains no egg protein 2
• Contact dermatitis to neomycin is NOT a contraindication—only anaphylactic reactions contraindicate vaccination 1
• Having a pregnant household member is NOT a contraindication for vaccinating other family members 1

Clinical Rationale: Why Two Doses Matter

The shift to two-dose vaccination was necessitated by real-world experience showing that one-dose vaccination coverage of 96-99% was insufficient to prevent school outbreaks. 3 Breakthrough varicella in vaccinated persons, though typically mild, remains contagious and sustains transmission. 1, 3 The substantial boost in antibody titers after the second dose (>10-fold increase in geometric mean titers) provides the additional protection needed to prevent both individual disease and community transmission. 1