Just in case any of you have a measles exposure in your facility, I thought I’d share with you the information I just sent out to California hospitals.

Many of you are dealing with healthcare worker exposures to measles.  Anyone with two documented doses of MMR vaccine is presumed to be immune and no additional MMR doses are recommended at this time, nor is serologic testing recommended for such persons.  However, we have received a number of questions about healthcare workers who were exposed to measles and did not have available immunization records so they received serologic testing for measles and were found to be IgG negative or equivocal.  Later the healthcare worker found records documenting that they had had two doses of measles-containing vaccine.  The question then is – can the person presumed to be immune or not?  At this point in time, the CDC recommendation is to trust the vaccine record over serology results.  This is because serology may not detect antibody that is present and would be boosted in the event of an exposure.  The following information comes from the CDC/ACIP statement of MMR vaccine and below that is the question I asked the CDC measles SME about this recommendation and the response.

 

 

Prevaccination antibody screening before measles, rubella, or mumps vaccination for health-care personnel who do not have adequate presumptive evidence of immunity is not necessary unless the medical facility considers it cost effective. For health-care personnel who have 2 documented doses of measles- and mumps- containing vaccine and 1 documented dose of rubella-containing vaccine or other acceptable evidence of measles, rubella, and mumps immunity, serologic testing for immunity is not recommended. If health-care personnel who have 2 documented doses of measles- or mumps- containing vaccine are tested serologically and have negative or equivocal titer results for measles or mumps, it is not recommended that they receive an additional dose of MMR vaccine. Such persons should be considered to have acceptable evidence of measles and mumps immunity; retesting is not necessary. Similarly, if health-care personnel (except for women of childbearing age) who have one documented dose of rubella-containing vaccine are tested serologically and have negative or equivocal titer results for rubella, it is not recommended that they receive an additional dose of MMR vaccine. Such persons should be considered to have acceptable evidence of rubella immunity.

 

The 2013 ACIP MMR guidance states that if HCP with two documented doses of MMR vaccine are inadvertently tested for measles immunity and found to be measles IgG negative or equivocal, that they be considered immune.  During this outbreak we’ve had a number of situations in which HCP were exposed and could not locate their immunization records so serology was done and was negative.  Then they would somehow locate their records documenting two doses of MMR vaccine and want to go back to work.  Different jurisdictions have handled these situations differently and some have not been permitted vaccinated, but IgG negative HCP to go back to work.  We’ve provided the ACIP guidance but it seems likely that this guidance was written for pre-employment screening purposes, not for workups of actual measles exposures.  We understand that although a person might be IgG negative or equivocal at the time of testing, an exposure to measles might boost the IgG to protective levels. 

 

CDC’s response: Yes, we’ve been asked a number of times during this measles outbreak to date and that has been our response.  This guidance was also intended for outbreak response.  The table in the ACIP statement that summarizes measles evidence of immunity is used for making decisions regarding vaccination in outbreak response as well as pre-exposure vaccination.  I understand the concerns when faced with a negative test but test results can be false positive and negative and seroprevalance does not equate exactly with immunity (we use PRN results as a correlate of protection).  We’ve had measles cases occur in HCPs documented to have antibodies prior to vaccination.  Those without detectable antibodies may have cell immune response that can be rapidly activated on exposure.  So, we’d suggest sticking with the ACIP recommendations.  If we see failures (cases) due to these policies, this could inform future revision.

Kathleen Harriman, PhD, MPH, RN

Chief, Vaccine Preventable Diseases Epidemiology Section

Immunization Branch

California Department of Public Health

850 Marina Bay Parkway

Building P, Second Floor

Richmond, CA 94804

 

Office)  510-620-3767

Cell)       651-699-2970

Fax)        510-620-3949