Hi Ed,
You’re correct, the IgG assay does not reliably reflect a vaccinated person’s true immune memory. That’s why it is not recommended to check IgG in people who are fully vaccinated
(for HCP this means 2 doses of live vaccine) including post exposure. In the event a post-vaccination IgG is drawn and is not positive, recommendations are to ignore that and consider the person immune based on their vaccination history.
Yes, breakthrough measles infections are possible but rare, and typically mild when they do occur in immunocompetent adults. For the situation you describe below, assuming
the worker is not severely immunocompromised, work exclusion would not be necessary, regardless of the IgG that was done.
Melanie
Melanie Swift, MD, MPH
Professor of Medicine
Vice Chair, Division of Public Health, Infectious Diseases and Occupational Medicine
Medical Director,
Mayo Clinic
Physician Health Center
Associate Medical Director, Occupational Health Service
Vice Chair, Institutional Biosafety Committee
_______________________________
Mayo Clinic
200 First Street SW
Rochester, MN 55905
From: MCOH-EH <mcoh-eh-bounces@mylist.net>
On Behalf Of Galaid, Edward via MCOH-EH
Sent: Friday, August 1, 2025 10:20 AM
To: mcoh-eh@mylist.net
Cc: Galaid, Edward <Edward.Galaid@rsfh.com>
Subject: [EXTERNAL] [MCOH-EH] Testing for measles immunity
A Charleston hospital had a suspected case of measles in their ED. One of the HCWs who had direct contact with kid, was fully vaccinated was found to have an indeterminate IgG result (by report).
She received a dose of vaccine and it’s anticipated that she will be excluded from work from day 5-21 per the CDC guidance.
I’ve started reading about waning immunity to MMR among those who received their primary series of vaccine, and also about the performance of the measles-specific IgG immunoassays. Check out: Latner et
al Qualitative Variation among Commercial Immunoassays for Detection of Measles-Specific IgG
J Clin Microbiol
. 2020 May 26;58(6):e00265-20. This study reports an 11% false negative rate.
In fully vaccinated adults with negative IgGs, is it valid to retest with a different kit? The authors concluding
statement “ Individuals that have negative or equivocal results for measles IgG should be vaccinated or revaccinated (6).
In some cases, vaccination is not possible and testing with a second line diagnostic assay may be necessary to determine immune status.”
Oh, and by the way, if we exclude someone from work, waiting to see if they blossom forth with a rash… how are we going to deal with missed wages?
Ed Galaid
Edward I. Galaid, MD, MPH, FACOEM
ABIM, ABPM (OM)
Medical Director, Occupational Medicine
Roper St. Francis Healthcare, Charleston SC
Chair, Public Safety Medicine Section, American College of Occupational and Environmental Medicine
NFPA 1580 Technical Committee on Emergency Responders Occupational Health
5070 International Blvd Ste. 131 North Charleston, SC 29418
843-402-5053 (O)
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