What IgG (Immunoglobulin G) titer levels indicate immunity to Measles, Mumps, and Rubella (MMR)?

MMR Immunity Titers: Interpretation and Clinical Thresholds

Any detectable antibody level above the standard positive cutoff value of the licensed assay being used indicates immunity to measles, mumps, and rubella. 1

Measles Immunity Assessment

For measles, any detectable antibody by enzyme immunoassay (EIA/ELISA) or other licensed serologic test indicates immunity. 1

• Modern EIA/ELISA assays have replaced the older hemagglutination-inhibition (HI) test and are more sensitive for detecting measles antibodies 1
• Persons with measles-specific antibody detectable by any serologic test are considered immune 1
• The seroresponse threshold used in clinical trials was 255 mIU/mL for anti-measles virus antibodies, with at least 94% of vaccinated children achieving levels above this threshold 2
• Equivocal results should be treated as susceptible unless documentation of adequate vaccination or subsequent testing confirms immunity 1

Rubella Immunity Assessment

For rubella, any antibody level above the standard positive cutoff of the licensed assay confirms immunity. 1

• The presence of serum rubella IgG is the only reliable evidence of previous rubella infection or immunity 1
• Clinical diagnosis of rubella is unreliable and should not be used to assess immune status 1
• The seroresponse threshold used in clinical trials was 10 IU/mL for anti-rubella virus antibodies, with at least 98% of vaccinated children achieving protective levels 2
• Persons with equivocal serologic results should be considered susceptible unless they have evidence of adequate vaccination or subsequent testing indicates immunity 1
• Laboratories that regularly perform antibody testing provide the most reliable results due to standardized reagents and procedures 1

Special Considerations for Rubella

• Occasionally, persons with documented rubella vaccination histories have IgG levels that are not clearly positive by ELISA 1
• Such persons can be administered a dose of MMR vaccine and need not be retested for serologic evidence of rubella immunity 1
• For women of childbearing age, birth before 1957 is not acceptable evidence of rubella immunity, as it provides only presumptive evidence and does not guarantee immunity 1

Mumps Immunity Assessment

For mumps, the demonstration of mumps IgG antibody by any commonly used serologic assay is acceptable evidence of immunity. 1

• The seroresponse threshold used in clinical trials was 10 EU/mL for anti-mumps virus antibodies, with at least 97% of vaccinated children achieving protective levels 2
• Persons with equivocal serologic test results should be considered susceptible unless they have other evidence of mumps immunity or subsequent testing indicates immunity 1
• Laboratory testing for mumps susceptibility before vaccination is not necessary during outbreaks 1

Practical Testing Approach

Timing of Specimen Collection

• For measles IgM: Blood should be collected during the first clinical encounter, may be detectable at rash onset, peaks at approximately 10 days after rash onset, and remains detectable for 30-60 days 3, 4
• If measles IgM is not detected within the first 72 hours after rash onset, collect a second specimen at least 72 hours after rash onset 3, 4
• For rubella IgM: Blood can be obtained as early as 1-2 days after rash onset, peaks at approximately 7 days, and remains detectable for 4-12 weeks 3
• If rubella IgM is not detectable in the first specimen, collect a second specimen 5 days after rash onset 3

Common Pitfalls to Avoid

• False-positive IgM results can occur with parvovirus infection, acute infectious mononucleosis, cytomegalovirus, or in persons who are rheumatoid factor positive 1, 4
• In low-prevalence settings, the likelihood of false-positive IgM results increases significantly 4
• Confirmatory testing using the direct-capture IgM EIA method is recommended when IgM is detected in a patient with no identified source of infection and no epidemiologic linkage to a confirmed case 4
• Specimens collected too early (within 72 hours of rash onset for measles) may yield false-negative results 3, 4

Antibody Persistence After Vaccination

• Neutralizing and ELISA antibodies to measles, mumps, and rubella viruses remain detectable in 95-100%, 74-91%, and 90-100% of individuals respectively, 11 to 13 years after primary vaccination 2
• Postinfection immunity to rubella appears to be long-lasting and probably lifelong 1
• Although vaccine-induced rubella antibody levels may decline with time, surveillance data suggest that waning immunity with increased susceptibility to rubella disease does not occur 1