MMR Vaccination Minimum Interval for Adults
The minimum interval between two doses of MMR vaccine for adults is 28 days (4 weeks). 1, 2, 3
Recommended Dosing Interval
Adults aged ≥13 years require a minimum of 4 weeks (28 days) between the first and second MMR doses. 2, 3, 4
This 28-day minimum interval is based on the fundamental principle that live virus vaccines not administered simultaneously should be separated by at least 1 month. 1
The CDC explicitly states that for persons aged >13 years, the recommended minimum interval is 4 weeks, which differs from the 3-month minimum recommended for children aged 12 months to 12 years. 1
Clinical Context and Rationale
The second dose is not a booster but addresses primary vaccine failure in the small proportion of persons who fail to respond immunologically to one or more components of the first dose. 1
Almost all persons who do not respond to the measles component of the first dose will respond to the second dose, with similar expectations for rubella and mumps components. 1
Two doses of MMR vaccine are necessary to develop adequate population immunity and prevent outbreaks, particularly in high-risk settings like healthcare facilities and educational institutions. 1, 3
High-Risk Adults Requiring Two Doses
Adults at increased risk who should receive two doses (separated by ≥28 days) include: 3
- Students in postsecondary educational institutions 3
- Healthcare personnel 3
- International travelers 3
- Adults in outbreak settings or recently exposed to measles 3
- Adults vaccinated with killed measles vaccine or vaccine of unknown type between 1963-1967 3
Important Clinical Pitfall
If the second dose is inadvertently administered before 28 days have elapsed, it should not be counted as valid and must be repeated after the appropriate interval has passed. 1
However, if more than 8 weeks elapse after the first dose, the second dose may be administered without restarting the schedule. 1
For healthcare workers born before 1957, birth year alone does not confer presumed immunity—documented immunity or vaccination with two doses is required. 3, 5