From the Research
The maximum recommended interval between the first and second doses of the varicella vaccine is not restricted by an upper limit, and the second dose can be administered at any time after the first dose, without the need to restart the series. This flexibility is supported by the most recent and highest quality study, which found that a 3-year interval between the two vaccine doses resulted in a higher geometric mean concentration (GMC) of antibodies compared to 1-year and 5-year intervals 1. The study, published in 2023, assessed the immunogenicity of two doses of the varicella vaccine at varying intervals and found that the optimal time point for the second dose is 3 years after the first vaccination.
Key Points
- The varicella vaccine series can be completed with a flexible interval between doses, prioritizing completion of the two-dose series for optimal protection against chickenpox.
- Even a single dose provides significant protection (about 80-85% effective against any varicella disease), and the immune system maintains memory cells that respond to the second dose regardless of the time elapsed.
- Completing the two-dose series is important as it provides optimal protection (approximately 98% effective) against chickenpox.
- The standard schedule calls for the second dose to be given 3-5 years after the first dose for children, or 4-8 weeks after the first dose for people 13 years and older, but delayed doses should be given at the earliest opportunity without restarting the series.
Evidence Summary
The evidence from the studies 1, 2, 3, 4, 5 supports the flexibility of the varicella vaccine schedule, with the most recent study 1 providing the strongest evidence for the optimal timing of the second dose. The studies consistently show that two doses of the varicella vaccine provide optimal protection against chickenpox, and that the immune system maintains memory cells that respond to the second dose regardless of the time elapsed.