The varicella vaccine protects against the varicella-zoster virus (VZV), which causes chickenpox. This live-attenuated vaccine stimulates immunity without causing the full disease. The vaccine is highly effective at preventing VZV infection and nearly eliminates the risk of severe complications, hospitalizations, and death from chickenpox. Current medical consensus recommends two doses of the varicella vaccine as the standard for maximum, long-lasting protection.
The Recommended Varicella Dosing Schedule
The routine vaccination schedule involves administering the varicella vaccine in two separate doses during childhood. The first dose is typically given to children between 12 and 15 months of age, often coinciding with other routine well-child visits. This initial injection begins the process of building protective antibodies within the immune system. The second dose is then recommended for children between 4 and 6 years of age, usually before they enter kindergarten or first grade. The second dose is sometimes given as part of a combination vaccine, known as MMRV, which also protects against measles, mumps, and rubella.
Understanding Why a Second Dose is Necessary
The transition from a single dose to a two-dose schedule was driven by scientific evidence showing a significant increase in protection. While a single dose provides an estimated 82% effectiveness against chickenpox, two doses boost this effectiveness to approximately 92% to 98%. This difference represents a substantial increase in the likelihood of a child remaining completely protected. The second dose acts as an immune “booster,” ensuring that a greater percentage of vaccinated individuals develop high levels of protective antibodies. This boosted immune response is also more durable, meaning the protection lasts longer over time and reduces the chance of a mild infection later in childhood. A primary goal of the second dose is to significantly reduce the occurrence of “breakthrough” cases, and the two-dose schedule is nearly 100% effective at preventing severe cases, including those that lead to hospitalization.
Addressing Gaps in Varicella Immunization
For individuals who missed the standard childhood schedule, a catch-up plan is available to ensure they achieve full protection. Those 13 years of age and older who have no evidence of immunity require two doses, separated by a minimum interval of 4 to 8 weeks. Children younger than 13 years old who are catching up should have at least three months between the first and second doses. If the recommended interval between doses has been exceeded, the vaccination series does not need to be restarted; the second dose can simply be administered at the next available opportunity. Adults who are not immune to VZV are also encouraged to receive two doses, especially if they are health care personnel or parents of young children.