The resurgence of measles continues to vex employee health professionals, as recently published research emphasizes that even immunized healthcare workers can still acquire the virus and expose co-workers and patients.1

The take-home message: Workers with a history of measles vaccination or immunity should wear an N95 or equivalent respiratory protection when examining or caring for patients with suspected or confirmed measles, says Shruti K. Gohil, MD, MPH, lead author of the study and associate medical director of Epidemiology & Infection Prevention at the University of California Irvine School of Medicine.

“You can acquire it even though you have been vaccinated, and the impact of not wearing an N95 for infection prevention in terms of exposures is huge,” she says. “You can expose a lot of patients and cause a lot of worry about transmission.”

There is about a 3% risk of breakthrough infections even after measles immunization, so the Centers for Disease Control and Prevention recommends wearing a respirator even if vaccinated when caring for patients with suspect or confirmed measles.

“I work in partnership with our hospital occupational health folks in making sure that all of our healthcare workers are immunized — making sure the people who are sick are not working while they are actively ill — and that they are in compliance with infection prevention practices,” Gohil says. “One of the things we have difficulty with sometimes is that our healthcare workers will ask us, ‘How come I have to wear an N95 if I am already vaccinated against measles?’”

With measles declared eradicated in the U.S., in 2000 it fell off the clinical radar, leading to misdiagnoses and unrecognized cases as it began dramatically returning a decade later. The infected workers in this outbreak were exposed primarily through face-to-face contact with undiagnosed cases of measles, though given the patient symptoms, N95 respiratory protection was probably warranted. Yet N95 respirator use by healthcare workers with documented immunity to measles is not uniformly required or practiced in hospitals, the authors observe.

“We know it’s not standardized practice to use N95s if you have been vaccinated against measles,” Gohil says. “They should wear N95s as soon as there is concern about potential measles in a patient. Recognizing those infected early [and following precautions] allows you to use resources appropriately. Your time and energy can go toward taking care of the patient as opposed to chasing down all the healthcare workers who may have exposed other patients.”


A community outbreak of measles in Orange County, CA, in 2014 led to secondary transmission to five healthcare workers. Of these, four had direct contact with measles patients and none wore N95 respirators. Four of the healthcare workers had prior evidence of immunity and continued working after developing symptoms, ultimately resulting in 1,014 exposures to patients and colleagues.1

“They had proof of immunity, but still got sick,” Gohil says. “They were very mild symptoms — that was pretty striking. They hardly knew that they were sick. You usually have symptoms of fever, cough, and cold-like symptoms. These healthcare workers had very little or none of that. The reason they continued to work is that they really didn’t feel that they were sick. It wasn’t until the [measles] rash showed up that clinicians were aware that something else was going on and that’s when they reported for care.”

Despite the relatively mild nature of the occupational infections, it certainly could not be assumed that transmission would not continue. Due diligence required the herculean follow-up of all exposures, none of whom contracted measles.

“In the literature we know that if you are vaccinated you are less likely to acquire measles, and it would make common sense that the presence of antibodies would limit the course of the illness and the likelihood that you would transmit to others,” she says. “We have hints and suggestions that this is true, but the fact that we had four symptomatic healthcare workers who saw all these other patients while they were actively infected resulted in a whole bunch of exposures. None of the exposures went on to acquire disease, and that is important to note.”

Thus, in an experiment of sorts that would never be approved as a clinical trial, the outbreak showed the vaccine is imperfect but it did apparently block subsequent transmission. “So as far as we know, this is one of the few opportunities to [assess] the vaccine efficacy in limiting illness and preventing transmission.”

The outbreak could serve as a teachable moment for employee health professionals.

“Since re-emerging global and domestic infectious diseases like measles are a real risk to healthcare workers — even with former immunity status — and because measles symptoms can present like other infectious diseases, it is important that healthcare workers wear respirators when evaluating these types of patients prior to diagnosis,” says Amber Mitchell, DrPh, MPH, CPH, president and executive director of the International Safety Center.

Healthcare workers who have rarely seen a measles case may assume they are immune if they have been vaccinated or had natural infection as a child. Thus, they may feel safe treating confirmed or suspect measles patients without respiratory protection and may even decide to disregard a hospital policy.

“I think most of hospitals do have these [N95] policies in place, but in practice they may see some resistance to this type of policy,” Gohil says. “I can say at my hospital, UC Irvine, we did have something in place for use of N95s.”

In addition, although most healthcare workers are required to have evidence of measles immunity as a condition of employment, enforcement of such policies is variable, the authors noted. Infection control and occupational health strategies often treat historical documentation of measles immunity as absolute, despite the low but present risk for measles infection in persons with evidence of immunity, the authors concluded.

While examining suspect cases is more of a gray area, immunized workers would certainly be expected to wear respirators to enter the room of a diagnosed measles patient under airborne precautions. Though they use powered air purifying respirators (PAPRs) instead of N95s, the policy at UnityPoint Health-Methodist/Proctor Hospital in Peoria, IL, calls for full precautions regardless of immune status, says Mary Bliss, RN, COHN, Coordinator of Employee Health Services at the hospital.

“We check MMR vaccine verification and/or titer results on all new hires coming into our hospital,” she tells Hospital Employee Health. “Annually, every employee has to complete the infection control training modules. One of the training modules addresses types of diseases, measles included, and the type of isolation room, protective equipment, precautions, that are required before entering the room. It is expected that any employee going into one of the rooms where there is a patient with a diagnosis of measles would follow the precautions for that type of isolation room — even if the employee has had two MMR vaccines or a titer verifying their immunity. It would be considered a policy violation to not follow the precautions.”

The community outbreak in Orange County included 17 confirmed cases diagnosed from mid-January 2014 to April 21. The first identified measles case was a 19-year-old female with known exposure to measles during travel to the Philippines who developed disease despite three documented MMR vaccine doses. One cluster in the outbreak included a “vaccine-refusing family” which led to subsequent spread in a daycare center. As cases presented for care, a history of immunity provided “false reassurance” to healthcare workers with unprotected face-to-face exposures, leading them to continue working even when mild symptoms appeared.

“Our findings emphasize the importance of adherence to the recent CDC recommendation for use of N95 or equivalent respirator for suspect measles cases regardless of immunity status,” Gohil and colleagues concluded.

That may present a challenge for primary care facilities that frequently do not stock N95 respirators or have their staff fit-tested. Again, even facilities with policies in place still depend to some degree on the ability to recognize the rare but returning disease.

“Timely N95 respirator use relies on provider suspicion of measles, which may not be appreciated until after direct contact with infected patients, particularly in post-elimination era settings where clinical experience with measles is low,” the researchers noted. “In our study, 80% of patients required multiple visits before diagnosis. This finding underscores the need for continued, periodic education on previously eliminated diseases of front-line healthcare workers.”

After the outbreak, the facility began immediate triage of patients presenting with any rash, using signage to guide patients to enter the facility away from the emergency room waiting area and directly into airborne isolation until further evaluation.


  1. Gohil SK, Okubo S, Dickey L, et al. Healthcare Workers and Post-Elimination Era Measles: Lessons on Acquisition and Exposure Prevention. Clin Infect Dis 2016;62:166-172.