What is the four-day grace period and when can it be used?
CDC and ACIP allow a 4-day grace period. If a vaccine is given up to 4 days before the minimum recommended age or interval for administration of the vaccine, it can be counted as valid. However, this does not apply to every vaccine and does not change the recommended schedule for routine vaccine administration. The 4-day grace period does not apply to the minimum 28-day interval between 2 live virus vaccines (MMR, LAIV and Varicella).