What is the recommended dose and route of administration for Varilrix (varicella vaccine)?

Varilrix Vaccine Dosing and Administration

Varilrix should be administered as a 0.5 mL dose given subcutaneously, with children 12 months through 12 years receiving two doses separated by at least 3 months, and persons ≥13 years receiving two doses separated by at least 4 weeks. 1, 2

Dose Volume and Route

• Each dose of Varilrix is 0.5 mL administered subcutaneously 1, 2
• The subcutaneous route is the recommended and approved administration method for all varicella vaccines 1
• While inadvertent intramuscular administration does not require revaccination, subcutaneous injection remains the standard route 3

Two-Dose Schedule by Age Group

Children 12 Months Through 12 Years

• First dose: administer at 12-15 months of age 1, 2
• Second dose: administer at 4-6 years of age (before school entry) 1, 2
• Minimum interval between doses: 3 months 1, 2
• If the second dose is inadvertently given between 28 days and 3 months after the first dose, it is considered valid and does not need repeating 1, 2
• The second dose may be administered earlier than 4-6 years, provided the 3-month minimum interval is maintained 1, 2

Adolescents and Adults ≥13 Years

• Two 0.5 mL doses separated by a minimum of 4 weeks (28 days) 1, 2
• The 4-8 week interval is optimal, though doses given ≥28 days apart are acceptable 1
• All persons ≥13 years without evidence of immunity should receive both doses 1

Vaccine Preparation and Storage

• Varilrix must be stored frozen at -15°C (5°F) or colder 1
• The diluent should be stored separately at room temperature or refrigerated 1
• After reconstitution, the vaccine must be used within 30 minutes 1
• Reconstitute according to package insert directions immediately before administration 1

Clinical Efficacy of Two-Dose Regimen

• Two doses provide 98.3% vaccine efficacy compared to 94.4% for a single dose 1, 2
• Recipients of two doses are 3.3-fold less likely to experience breakthrough varicella 1, 2
• After two doses, >99% of children achieve protective antibody levels (≥5 gpELISA units/mL) compared to 76-85% after one dose 1, 2
• The second dose produces a greater-than-tenfold boost in antibody titers when measured 6 weeks post-administration 1

Special Populations

Household Contacts of Immunocompromised Persons

• Children <13 years receive one 0.5 mL dose subcutaneously 4
• Those ≥13 years receive two 0.5 mL doses 8 weeks apart 4
• Vaccination is safe and immunogenic in this population, with seroconversion rates approaching 100% 4

Immunocompromised Children with Cancer

• Two doses of Varilrix given 3 months apart can be administered to cancer patients in remission 5
• Seroconversion rate is 19% after one dose but increases to 94% after the second dose 5
• Vaccination should occur during maintenance chemotherapy for leukemia or 3-6 months after treatment discontinuation for solid tumors 5

Critical Implementation Points

• All children entering school must have received two doses or have other evidence of immunity due to high transmission risk in school settings 1, 2
• The 3-month interval for children is based on clinical trial design that demonstrated optimal immunogenicity 1
• Healthcare personnel, college students, and other high-risk adults without evidence of immunity require priority two-dose vaccination 2
• Varilrix can be safely administered concomitantly with other routine childhood vaccines without compromising immunogenicity 6

Common Pitfalls to Avoid

• Do not delay the second dose beyond the recommended 4-6 year timeframe without reason, as varicella incidence and outbreaks are higher among elementary school-aged children 1, 2
• Do not restart the vaccine series regardless of time elapsed between doses; simply continue with the next scheduled dose 2
• Do not use combination MMRV vaccine for persons ≥13 years, as it is only licensed for children 12 months through 12 years 1, 2
• Avoid salicylates for 6 weeks after vaccination due to Reye syndrome risk 2