What is the dose and route of administration for varicella (chickenpox) vaccine, and which vaccine, such as Varivax (varicella vaccine) or ProQuad (measles, mumps, rubella, and varicella vaccine), is used?

Varicella Vaccine Dosing and Administration

The varicella vaccine is administered as a 0.5 mL dose given subcutaneously (or intramuscularly), using either single-antigen Varivax for all ages ≥12 months or combination ProQuad (MMRV) for children aged 12 months through 12 years only. 1, 2

Dose and Route

• Each dose is 0.5 mL administered subcutaneously 1, 2
• The FDA label for Varivax specifies that intramuscular administration is also acceptable 2
• Research confirms that inadvertent intramuscular administration produces equivalent immunogenicity to subcutaneous injection and does not require revaccination 3

Available Vaccine Products

Single-Antigen Varicella Vaccine (Varivax)

• Approved for all individuals ≥12 months of age, including adolescents and adults 1, 2
• Contains minimum 1,350 plaque-forming units (PFUs) of Oka/Merck varicella-zoster virus per 0.5 mL dose 1
• Must be used for persons ≥13 years since MMRV is not licensed for this age group 1, 4

Combination MMRV Vaccine (ProQuad)

• Approved only for children aged 12 months through 12 years 1, 4
• Contains higher varicella titer (minimum 3.99 log10 PFUs) compared to single-antigen vaccine 1, 5
• Provides simultaneous protection against measles, mumps, rubella, and varicella 1, 5
• Preferred over separate injections when all components are indicated and none are contraindicated, particularly for children ≥48 months (4 years) of age 6

Two-Dose Schedule

Children 12 Months Through 12 Years

• First dose at 12-15 months of age 1, 4, 2
• Second dose at 4-6 years of age (before school entry) 1, 4, 2
• Minimum interval between doses is 3 months 1, 4
• If the second dose is inadvertently given 28 days to 3 months after the first dose, it is considered valid and does not need repeating 1

Adolescents and Adults ≥13 Years

• Two 0.5 mL doses separated by minimum 4 weeks (28 days) 1, 4, 2
• Only single-antigen Varivax may be used in this age group 1, 4

Vaccine Selection Algorithm

For children 12 months through 12 years:

• If measles, mumps, and rubella vaccines are also needed and not contraindicated, use ProQuad (MMRV) 1, 6
• If only varicella vaccine is needed, use Varivax 1
• Important caveat: For children 12-23 months receiving their first measles-containing vaccine, there is increased risk of febrile seizures with MMRV compared to separate MMR and varicella vaccines; this risk does not apply to children ≥4 years 6

For adolescents and adults ≥13 years:

• Use only single-antigen Varivax, as ProQuad is not licensed for this age group 1, 4

Clinical Efficacy of Two-Dose Regimen

• Two doses provide 98% efficacy against any varicella disease and 100% efficacy against severe disease, compared to 94% efficacy with one dose 1, 7
• Recipients of two doses are 3.3-fold less likely to experience breakthrough varicella compared to one-dose recipients 1, 4
• After two doses, >99% of children achieve protective antibody levels (≥5 gpELISA units/mL) 1
• The second dose produces a substantial boost in varicella antibody titers, increasing from geometric mean titer of 13.0 to 588.1 gpELISA units/mL 8

Critical Administration Details

• Administer immediately after reconstitution; discard if not used within 30 minutes 2
• Use only the supplied sterile diluent, as it contains no preservatives or antiviral substances that could inactivate the vaccine virus 2
• Do not combine with any other vaccine through reconstitution or mixing 2
• Avoid salicylates for 6 weeks following vaccination in children and adolescents due to Reye syndrome risk 4, 2

Common Pitfall to Avoid

Do not assume that MMRV (ProQuad) can be used in adolescents or adults—it is only licensed for children 12 months through 12 years, and attempting to use it outside this age range would be off-label 1, 4.