Mumps outbreak sparks HCW vaccine questions and public health debate

Hospitals should check HCWs' immune status

An outbreak of mumps in Iowa has led hospitals to re-examine the immunization records of health care workers, with some checking for serologic evidence of immunity in employees who have had an exposure.

With more than 975 reported cases of mumps in Iowa alone and the disease spreading throughout the central states, the Centers for Disease Control and Prevention (CDC) has advised health care workers to have two doses of the MMR (measles, mumps, rubella) vaccine.

"If you have not received two doses of the mumps vaccine, it is very important that you get your second dose," CDC director Julie L. Gerberding, MD, MPH, said in a press conference, emphasizing the importance of health care worker immunization. The CDC is using MMR doses from the national stockpile, as well as donated doses from the manufacturer, Merck, to supplement the states' supply.

Health care workers who contract mumps should stay home until they are symptom-free, public health authorities advise.

The Iowa Department of Public Health previously had advised hospitals to review the immunological status of their staff, says Patricia Quinlisk, MD, state epidemiologist. Employees should have had mumps or two doses of the mumps vaccine, which usually is given with measles and rubella vaccines in the MMR, she says.

Hospitals in affected areas have responded with employee health efforts. The University of Iowa Hospitals and Clinics in Iowa City is testing the titers of employees who have been exposed and giving them a second MMR vaccine if they only had one. Health care workers with direct patient care responsibilities in high-risk areas also have received a second dose of MMR if they had only one.

A few health care workers have contracted mumps despite the vaccine, probably due to the small margin of vaccine failure, says Cheryl Person, RN, BSN, nurse manager of the University Employee Health Clinic. So far, all exposed health care workers who were tested had a positive titer, showing evidence of immunity, she says.

The mumps outbreak has puzzled public health officials and led to greater scrutiny of vaccine effectiveness and vaccination policies. Iowa typically has about five cases of mumps a year. But the state is now ground zero for the largest epidemic of mumps in the United States since 1988, according to the CDC.

"We're trying to figure out what is contributing to this. We don't have all the answers," Quinlisk says.

She notes that the vaccine is about 95% effective — that still leaves five people per hundred who are susceptible to the disease. Also, Iowa began requiring two doses of the MMR vaccine for schoolchildren in 1991. Many Iowans, including some health care workers, may have received only one dose of the vaccine.

Gerberding also reassured health care providers that the MMR vaccine is effective. "I really want to emphasize that while we are of course investigating the outbreak and we will learn more about the efficacy of the vaccine in this particular setting, we have absolutely no information to suggest that there is any problem with the vaccine," she said.

Air travel contributed to spread

The outbreak began in December with two confirmed cases of mumps in college students at an eastern Iowa university. Another case was confirmed in mid-January, and by February, cases were appearing on college campuses throughout the state. Cases also have been reported in nearby states, including Kansas, Nebraska, Illinois, Minnesota, Missouri, Wisconsin, and Oklahoma.

Air travel may have escalated the spread and could ultimately lead to outbreaks across the country. The CDC reported that two travelers — one going from Waterloo, IA, to Washington, DC, and the other from Tucson, AZ, to Cedar Rapids, IA — may have exposed other air passengers to mumps between March 26 and April 2. A 2005 epidemic in the United Kingdom, involving about 56,000 cases, also may be linked to the Iowa outbreak — the viruses in the outbreaks share the same genotype.

As of late April, Iowa had reported 975 confirmed, probable or suspect cases of mumps, a disease characterized by fever, headache, fatigue, and the telltale swelling of the salivary glands. About 25% of the Iowa cases have been among college students, with a median age of 21. About 20% to 30% of the cases may be asymptomatic, the CDC reports.

Before the vaccination became routine, "nearly everyone in the United States experienced mumps," the CDC says. Although complications are rare, the disease can lead to inflammation of the testicles or ovaries, meningitis or encephalitis, spontaneous abortion or deafness.

Until this outbreak, mumps was not a major vaccination concern. It is included in the MMR vaccine and routinely administered, but its vaccine partners, measles and rubella, were considered a greater potential hazard. "We haven't had a problem with mumps for years," says William Bellini, PhD, chief of the CDC's Measles, Mumps, Rubella and Herpes Virus Branch.

Is the vaccine effective?

If most people have had either the mumps or the vaccine, why did an outbreak occur? Does this indicate that the vaccine is not effective?

Some 64% of those with reported cases of mumps in Iowa had received two doses of the MMR vaccine, while 10% had received only one dose. But that doesn't necessarily reflect a vaccine failure, public health authorities say.

"It doesn't mean the vaccine's not working," Quinlisk says. "It just means the vaccine is not 100%." A significant outbreak can occur even with just five out of every 100 people susceptible to the disease despite vaccination, she says. "The best thing we can do is make sure everybody is fully vaccinated. You're going to slow down if not stop the spread," she says.

Still, the sudden spread of mumps has raised a number of public health questions. "We're wondering why we're seeing that now, [and] why we haven't seen it before," says Bellini. The CDC is looking into the possibility of waning immunity. Some colleges and universities required an additional dose of MMR before matriculation, but some smaller colleges did not, he says.

Gerberding noted that so far the CDC does not see evidence of waning immunity. "If waning immunity were a primary problem, we would expect much older people to be affected, at least those who did not have mumps when they were children," she said. "So we are looking into this as one of several possibilities, but I think right now with what we know about this vaccine's efficacy, what we know about the undervaccinated people in this age cohort, and what we know about the sociology of life in some of these [college] community settings, we have ample explanation for why the virus is spreading the way it is."

Meanwhile, there have been no outbreaks in hospitals, day care centers, or K-12 schools, Gerberding noted. "[F]ortunately, we are not seeing outbreaks right now in schools or in younger children in large part because they have a higher degree of two-dose coverage."

"The biggest lesson learned is that this could happen anywhere," says Quinlisk, who notes that Iowa's record of vaccination is similar to that of other states. "Now is a really good time to make sure that college campuses, health care workers, and the general population are fully vaccinated."