1. The recommended ages for routine first (at age 12-15 months) and second (at age 4-6 years) doses of varicella vaccine are harmonized with the recommendations for MMR vaccine use and intended to limit the period when children have no varicella antibody. The recommended age for the second dose is supported by the current epidemiology of varicella, with low incidence and few outbreaks among preschool-aged children and higher incidence and more outbreaks among elementary school-aged children.

2. Although, most studies are done when 2nd dose is given after 3 months of the first, there are few trials where the two schedules were compared and it was concluded that among children, VZV antibody levels and GMTs after 2 doses administered 4-6 years apart were comparable to those obtained when the 2 doses were administered 3 months apart (seroconversion: 99.2% vs 99.6%, GMTs: 212.4 vs 142.6, respectively).

3. However, the CMI responses measured by mean stimulation index (SI), a marker of cell-mediated immunity were 36.9 for 2nd dose after 3 months of primary dose, and 58.6 when 2nd dose was given at 4-6 yrs of age [2].