Does the 4-day “grace period” apply to the minimum age for administration of the first dose of MMR? What about the 28-day minimum interval between doses of MMR?

A dose of MMR vaccine administered up to 4 days before the first birthday may be counted as valid. However, school entry requirements in some states may mandate administration on or after the first birthday. The 4-day “grace period” also may be applied to the 28-day minimum interval between two doses of MMR if the interval is inadvertently shorter than 28 days, although you should never plan to administer the second dose earlier than the 28-day minimum interval. This 4-day “grace period” does not apply to the strict 28-day minimum interval between two different live vaccines (e.g., MMR and varicella vaccines), if not administered at the same visit.