MMR Vaccine Immunity and Antibody Titers Over Time
Yes, a person who has received two doses of MMR vaccine many years ago can still show up as not immune when antibody titers are drawn a decade later, despite having adequate protection against disease.
Understanding MMR Immunity After Vaccination
The Advisory Committee on Immunization Practices (ACIP) guidelines explain that antibody levels following MMR vaccination may decline over time, but this does not necessarily indicate loss of protection:
- Antibody decline is expected: Vaccine-induced antibody levels typically decline over time, but this does not equate to loss of protection 1
- Primary vs. secondary response: The second dose of MMR is not considered a booster but is given to produce immunity in the small proportion of people who failed to respond to the first dose 1
- Long-term protection: While antibody titers may wane, the clinical significance of this decline is generally limited 2
What Happens to MMR Antibodies Over Time
Research studies have documented the pattern of antibody decline after MMR vaccination:
- A 20-year follow-up study found that while antibody levels declined significantly after the second dose, 95% of vaccinees remained seropositive for measles, 74% for mumps, and 100% for rubella even two decades after vaccination 3
- Another study showed that people vaccinated ≥15 years prior had lower neutralizing antibody geometric mean titers (GMT of 58) compared to those vaccinated 1-5 years prior (GMT of 97), demonstrating antibody decay over time 4
Clinical Implications of Low Antibody Titers
When antibody titers are drawn years after vaccination and show as "not immune":
- Presumptive immunity still exists: ACIP considers documented vaccination with 2 doses of MMR as presumptive evidence of immunity, regardless of subsequent serologic test results 1
- Documented vaccination supersedes serology: For healthcare personnel with 2 documented doses of MMR vaccine who test negative or equivocal for mumps titers, no additional doses are recommended—they should still be considered immune 1
- Memory immune response: Even with low circulating antibodies, most vaccinated individuals maintain immune memory that can be rapidly activated upon exposure to wild virus
Recommendations for Those with Low Titers
If titers are drawn and show as "not immune" despite two prior MMR doses:
- Healthcare workers: If a healthcare worker has 2 documented doses of MMR vaccine and is later found to have negative or equivocal mumps titers, no additional dose is recommended 1
- General population: For most people with documented two-dose MMR vaccination, additional doses are not routinely recommended based solely on negative serology
- Special situations: During outbreaks or for high-risk exposures, additional doses might be considered regardless of antibody status
Important Caveats
- Mumps component shows most waning: Of the three components, mumps antibodies tend to wane most significantly, with only 74% remaining seropositive after 20 years 3
- Different testing methods: Different laboratories may use different cutoff values for determining immunity
- Anamnestic response: Studies show that most seronegative individuals with prior vaccination history can mount a strong anamnestic response when exposed to the virus or given an additional dose 4
In summary, while antibody titers may decline over time following MMR vaccination, documented receipt of two doses provides presumptive evidence of immunity that generally supersedes negative serologic findings years later. The immune system maintains memory cells that can rapidly respond to exposure even when circulating antibody levels are low.