Measles Titer Significance for Immunity Determination
A measles titer serves as laboratory evidence of immunity, but documented vaccination with 2 doses of MMR vaccine supersedes any subsequent serologic testing results—meaning individuals with proper vaccination documentation should be considered immune regardless of titer levels. 1, 2
Primary Role of Measles Titers
Measles titers function as one of four acceptable forms of presumptive evidence of immunity for healthcare personnel and other populations:
- Written documentation of 2 MMR doses administered ≥28 days apart 1
- Laboratory evidence of immunity (positive titer) 1
- Laboratory confirmation of disease 1
- Birth before 1957 1
Critical Clinical Principle: Vaccination Documentation Trumps Serology
For individuals with 2 documented MMR doses who test serologically negative or equivocal for measles, it is NOT recommended to administer an additional MMR dose—documented age-appropriate vaccination supersedes subsequent serologic testing results. 1, 2
This recommendation exists because:
- Almost all persons who don't respond to the first dose will respond to the second dose 2
- The two-dose schedule is specifically designed to capture primary vaccine failures 2
- Antibody titers can wane over time without loss of immune memory 2
- Approximately 1% of properly vaccinated individuals may still have low or undetectable titers but retain cellular immunity 1
When Prevaccination Titer Testing May Be Considered
Prevaccination antibody screening is not necessary unless the medical facility considers it cost-effective, though no recent cost-effectiveness studies exist 1. Key scenarios:
- Employee lacks adequate documentation of immunity 1
- During measles outbreaks: Serologic screening before vaccination is NOT recommended due to need for rapid vaccination 1
- For research purposes only: Routine serologic testing after documented vaccination is not recommended for clinical decision-making 2
Common Pitfalls to Avoid
Do not routinely order serologic testing after two documented MMR doses—this creates unnecessary confusion when titers return low or negative 2. The most frequent error is revaccinating based solely on negative titers in someone with proper documentation of two MMR doses 2.
Do not withhold work privileges from healthcare personnel with 2 documented MMR doses but negative titers—they should be considered to have presumptive evidence of measles immunity 1.
Antibody Kinetics and Interpretation
Research demonstrates that measles antibody titers can decline over time:
- Antibody may attenuate by approximately 0.014 per day after vaccination 3
- Titers may fall below protective levels (typically <16 EIA units) after approximately 704 days in some individuals 3
- However, this serologic decline does not necessarily indicate loss of protection due to persistent cellular immunity 2
Special Populations Requiring Titer Assessment
Immunocompromised patients represent the primary exception where titers may guide additional vaccination decisions: