Should This Adult Receive a Second MMR Dose?
Yes, this 43-year-old adult who received only one MMR vaccine at age 14 should receive a second dose now to ensure adequate protection against measles, mumps, and rubella.
Rationale for Recommendation
Current Vaccination Status
This individual received their single MMR dose at age 14, which means:
- The vaccine was administered after their first birthday, making it a valid first dose 1
- They were born after 1957 (currently 43 years old), placing them in the category requiring documented immunity 1
- They have only one documented dose when two doses are now the standard recommendation 1
Why Two Doses Are Necessary
Approximately 5% of individuals who receive only one dose of MMR vaccine fail to develop immunity to measles due to primary vaccine failure 1. The second dose is specifically designed to:
- Reduce the proportion of persons who remain susceptible because of primary vaccine failure 1
- Provide immunity to those who did not respond to the first dose 1
- Ensure comprehensive protection, as waning immunity is not a major cause of vaccine failure 1
Adult Vaccination Guidelines
The ACIP guidelines clearly state that persons born in 1957 or later who are aged ≥18 years should receive at least one dose of MMR vaccine unless they have documentation of vaccination with at least one dose OR other acceptable evidence of immunity 1. However, the contemporary standard has evolved to a two-dose schedule 1.
For adults at increased risk for exposure (international travelers, healthcare workers, college students), two doses administered at least 28 days apart are specifically recommended 1. Even for general adult populations, the trend has moved toward ensuring two-dose coverage 1, 2.
Practical Implementation
Vaccination Schedule
- Administer the second MMR dose now 1
- No minimum interval is required since the first dose was given 29 years ago (well beyond the 28-day minimum spacing) 1
- A single dose will complete the recommended two-dose series 1, 2
Expected Immune Response
After the second dose, this individual should achieve:
- 100% seroprotection rates for measles, mumps, and rubella 3
- Durable immunity that addresses any potential primary vaccine failure from the first dose 1, 4
Important Considerations
Safety Profile
- MMR vaccine has a proven history of safety and efficacy in adults 5
- The vaccine can be safely administered to adults without contraindications 1
- There is no harm in giving MMR to someone who may already be immune 1
Common Pitfall to Avoid
Do not assume that one dose given in adolescence provides adequate lifelong protection. While persons born before 1957 can generally be considered immune due to natural infection, those born in 1957 or later require documented two-dose vaccination or serologic evidence of immunity 1. The single-dose recommendation for adults was an older standard that has been superseded by the two-dose schedule 1.
Alternative Approach
If there is uncertainty about immunity status, serologic testing could be performed before vaccination 1. However, vaccination without serologic testing is more cost-effective and ensures immediate protection 1. There is no risk in vaccinating someone who is already immune 1.