How to Determine if MMR Vaccination is Needed After Measles Exposure
Check measles IgG antibody levels using a standard enzyme immunoassay (EIA/ELISA), and if the result shows any level above the positive cutoff (typically >300 mIU/mL), the patient is immune and does not need MMR vaccination. 1, 2, 3
Step-by-Step Algorithm for Assessing MMR Immunity
Step 1: Order Serologic Testing
- Order measles, mumps, and rubella IgG antibodies using any standard, licensed enzyme immunoassay (EIA/ELISA) 2, 3
- Any antibody level above the standard positive cutoff value is acceptable evidence of immunity 2
- For measles specifically, an IgG level >300.0 mIU/mL indicates robust immunity 1
- For mumps, an IgG level ≥98.6 is considered positive 1
- For rubella, an IgG level ≥22.80 is above the standard positive cutoff 1
Step 2: Interpret Results
If Positive (Above Cutoff):
- The patient is immune and does NOT need MMR vaccination 1, 2
- Laboratory evidence of immunity is definitive, regardless of vaccination history or birth year 1
If Negative or Equivocal:
- Consider the patient susceptible to measles unless they have other acceptable evidence of immunity 2
- Check for alternative evidence of immunity: written documentation of 2 doses of MMR vaccine administered at least 28 days apart 2
- If no documentation exists, administer one dose of MMR vaccine immediately—do not retest for serologic evidence afterward 3
Step 3: Special Considerations Based on Birth Year
Adults Born Before 1957:
- Generally presumed immune to measles, mumps, and rubella due to natural infection during childhood 4, 1
- However, 5-9% of those born before 1957 do not have detectable measles antibody, and about 6% lack rubella antibody 4
- Serologic testing can definitively confirm immunity regardless of birth year 1
Adults Born During or After 1957:
- Require documented evidence of immunity (laboratory confirmation or vaccination records) 4
- Two doses of MMR vaccine separated by at least 28 days is acceptable evidence for measles and mumps; one dose is sufficient for rubella 2
Critical Pitfalls to Avoid
Do NOT Use IgM Testing for Immunity Screening
- IgM testing is NOT appropriate for routine immunity screening—only use IgG 3
- As measles becomes rare, false-positive IgM results increase significantly in low-prevalence settings 3
- IgM is only used for diagnosing acute infection, not for determining immunity 3
Do NOT Ignore Documented Vaccination History
- For healthcare personnel with documented MMR vaccination who test negative or equivocal, documented age-appropriate vaccination supersedes the serologic results—they should still be considered immune 2
- Do not give additional doses based on serology alone if proper vaccination is documented 2
Do NOT Use Outdated Testing Methods
- Do not use hemagglutination inhibition (HI) testing, as it has been supplanted by more sensitive EIA assays 3
- When adults who appeared antibody-negative by older HI testing were retested with EIA, almost all (>95%) had detectable antibodies 3
When Vaccination is Indicated
Administer MMR vaccine if:
- Serologic testing shows negative or equivocal results AND no documented vaccination history exists 2, 3
- The patient is a healthcare worker, international traveler, or in another high-risk category without evidence of immunity 4
- The patient was exposed to measles and lacks evidence of immunity (post-exposure prophylaxis is 74% effective) 5
Contraindications to consider:
- Severe immunosuppression (HIV with CD4 count indicating severe immunocompromise, active malignancy, high-dose immunosuppressive therapy) 4
- Pregnancy (counsel women to avoid pregnancy for 4 weeks after vaccination) 4
- Recent receipt of immunoglobulin or blood products (wait appropriate interval) 4