What is the recommended dosage and administration schedule for the Varicella (chickenpox) vaccine, also known as Capox?

Varicella (Chickenpox) Vaccine Dosing and Administration

I need to clarify that "CAPOX" is not the varicella vaccine—CAPOX is a chemotherapy regimen (capecitabine + oxaliplatin) used for colorectal cancer. The varicella vaccine is marketed as Varivax (monovalent) or ProQuad (MMRV combination). If you're asking about the varicella vaccine specifically, here are the evidence-based recommendations:

Standard Two-Dose Schedule for Healthy Children

All healthy children should receive a routine two-dose varicella vaccination series, with the first dose at 12-15 months of age and the second dose at 4-6 years of age. 1

First Dose Timing

• Administer the first dose routinely at 12-15 months of age 1
• The vaccine is approved for use starting at 12 months of age 1
• Do not administer before 12 months of age

Second Dose Timing

• Routinely administer the second dose at 4-6 years of age (before entering prekindergarten, kindergarten, or first grade) 1
• This timing is strategically chosen because varicella incidence and outbreaks are higher among elementary school-aged children 1
• The second dose may be given earlier if needed, provided minimum intervals are met 1

Minimum Intervals Between Doses

For children 12 months through 12 years: The minimum interval is 3 months between doses 2, 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

For persons 13 years and older: The minimum interval is 4 weeks (28 days) between doses 1

• Adolescents and adults without evidence of immunity should receive two 0.5-mL doses separated by at least 28 days 1

Available Vaccine Formulations

• Monovalent varicella vaccine (Varivax): Approved for ages ≥12 months 1
• Combination MMRV vaccine (ProQuad): Approved only for ages 12 months through 12 years 1
• For persons ≥13 years: Only single-antigen varicella vaccine may be used 1

Route of Administration

• Varicella vaccine is recommended to be given subcutaneously 3
• However, inadvertent intramuscular administration produces equivalent immunogenicity (97% vs 100% seroconversion) and does not require revaccination 3

Critical Timing Rule for Live Vaccines

If administering varicella vaccine with MMR or other live parenteral vaccines, they must be given either on the same day OR separated by at least 28 days. 4

• Live virus vaccines given less than 28 days apart (but not simultaneously) may result in impaired immune response 4
• When given on the same day, immune responses are identical to vaccines given a month apart 4

Contraindications and Precautions

Absolute contraindications: 2

• History of severe anaphylactic reaction to vaccine components (neomycin or gelatin)
• Pregnancy
• Known altered immunity (HIV with CD4 <15%, hematologic/solid tumors, congenital immunodeficiency, long-term immunosuppressive therapy)
• High-dose systemic corticosteroids (≥2 mg/kg/day prednisone or ≥20 mg/day) for ≥14 days 2

Wait at least 1 month after discontinuing corticosteroid therapy before vaccinating 2

Special Populations

HIV-infected children: May receive vaccine if CDC class 1 with CD4 T-lymphocyte percentage ≥15%, using 2 doses of monovalent vaccine with a 3-month interval 2

Leukemic children in remission: Should not be routinely immunized; vaccination should only be undertaken with expert guidance and availability of antiviral therapy 2

Postexposure Prophylaxis

Unvaccinated persons exposed to varicella should receive vaccine within 3 days of exposure (up to 5 days may provide some benefit). 2

• Vaccination within 3 days is >90% effective in preventing varicella 2
• Vaccination within 5 days is approximately 70% effective in preventing varicella and 100% effective in modifying severe disease 2

Common Pitfalls to Avoid

• Do not administer live vaccines 1-27 days apart (except same day)—this reduces immune response 4
• Do not use MMRV (ProQuad) in persons ≥13 years—only monovalent varicella vaccine is approved 1
• Do not restart the series regardless of time elapsed between doses 1
• Avoid salicylates for 6 weeks after vaccination due to Reye syndrome risk 2
• Egg allergy is not a contraindication—varicella vaccine contains no egg protein 2