Varicella Vaccine Second Dose Age

A 12-month-old infant is scheduled to receive immunizations during a well-child visit. The healthcare provider explains that the infant will receive the following vaccinations: Measles, Mumps, and Rubella (MMR) and Varicella (chickenpox). According to the Centers for Disease Control and Prevention (CDC) guidelines, the MMR vaccine should be administered at age 1 and again at age 4, while the Varicella vaccine is recommended at age 1, with a second dose between the ages of 4 to 6.

What is the recommended age for the second dose of the Varicella vaccine, expressed in years as the fill-in-the-blank answer?