When can a child receive Varivax (varicella vaccine) as a second dose after getting ProQuad (measles, mumps, rubella, and varicella vaccine) on September 2?

Timing for Second Dose of Varicella Vaccine After ProQuad

A child who received ProQuad on September 2 can receive Varivax as a second dose of varicella vaccine at least 3 months after the first dose, which would be December 2 or later. 1

Recommended Timing for Varicella Vaccine Doses

• For children 12 months through 12 years of age, the recommended minimum interval between two doses of varicella vaccine is 3 months 1
• 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
• For persons aged 13 years and older, the minimum interval between doses is 4 weeks (28 days) 1

Rationale for Timing Requirements

• The 3-month minimum interval recommendation for children is based on the design of studies evaluating 2 doses of varicella vaccine in children aged 12 months to 12 years 1
• This timing ensures optimal immune response to the second dose, as the immune system needs time to fully respond to the first dose before receiving a booster 2
• Two doses of varicella vaccine provide significantly better protection than a single dose:
  • Two-dose vaccine efficacy is 98% compared to 94% for a single dose 1
  • Recipients of 2 doses are 3.3-fold less likely to have breakthrough varicella compared to those who received only 1 dose 1

ProQuad and Varivax Interchangeability

• ProQuad (MMRV) and Varivax (varicella) vaccines contain the same varicella vaccine component, making them interchangeable for completing the varicella vaccine series 1, 3
• After receiving ProQuad as a first dose, Varivax can be used as the second dose of varicella vaccine 1, 3
• The second dose of varicella-containing vaccine significantly boosts varicella antibody titers, regardless of whether it's administered as ProQuad or Varivax 3

Clinical Benefits of Two-Dose Varicella Vaccination

• A two-dose varicella immunization schedule is recommended to achieve greater levels of immunity with fewer susceptible individuals 1
• Two doses provide greater protection against breakthrough varicella disease and reduce the number of outbreaks among school-aged populations 1
• After two doses, >99% of children achieve protective antibody levels against varicella, compared to 76-85% after a single dose 1

Common Pitfalls to Avoid

• Do not administer the second dose earlier than 28 days after the first dose, as this may result in suboptimal immune response 2
• Do not unnecessarily delay the second dose beyond the recommended interval, as this leaves the child vulnerable to breakthrough infection for a longer period 2
• Ensure proper documentation of both doses with dates to avoid unnecessary revaccination 2