As Arkansas outbreak ends, third MMR dose debate renewed

As Arkansas reigns in one of the largest outbreaks of mumps in the last three decades, there is renewed discussion about whether a third dose of the MMR (measles, mumps and rubella) vaccine is warranted.

The Center for Disease Control and Prevention’s (CDC) Advisory Council on Immunization Practices (ACIP) currently recommends two doses of MMR for children, and one to two doses for adults depending on their situation and needs. Two doses are recommended specifically for adults working in healthcare, traveling internationally or attending college, according to ACIP. As for a third, or booster dose, ACIP states that there is not sufficient data at this time either for or against a third vaccination to make a formal recommendation, although third doses have been given and found to be at least somewhat effective during recent outbreaks.

The CDC states that public health authorities may administer a third MMR dose for specifically targeted populations, but should first confirm whether the individual has already has two doses of the vaccine, if there is intense exposure to the facilitate transmission of the virus and if high attack rates are present.

“Additional data on the effectiveness and impact of a third dose of MMR vaccine for mumps outbreak control are needed to guide control strategies in future outbreaks,” according to CDC’s online guidance. “Authorities who decide to administer a third dose as part of mumps outbreak control are encouraged to collect data to evaluate the impact of the intervention.”

Some of the data that should be collected includes incidence of mumps in the target population, and the incidence of adverse events following a third dose.

Next: Unusual outbreak in Arkansas

‘Unusual’ outbreak in Arkansas

CDC representatives are on site at the Arkansas outbreak, and one of the things they may be investigating is what evidence, if any, might support a broader use of a third dose of the vaccine, said Dirk Haselow, MD, PhD, assistant professor of epidemiology at the University of Arkansas for Medical Sciences Fay W. Boozman College of Public Health and Arkansas state epidemiologist.

Haselow said Arkansas’ current outbreak accounts for about half of all the cases of mumps in the U.S. in 2016-now totaling 2,486 cases-and is the second largest outbreak in the last 25 years.

“This situation is very unusual and it shouldn’t be inferred that the vaccine is not working. What we have learned is that while we are seeing breakthrough disease it’s much milder than expected,” Haselow told Medical Economics.

In an outbreak of this size, Haselow said at least 500 cases of orchitis would be anticipated, but only 13 have been recorded, and no cases of central nervous system diseases like meningitis have been reported, either.

The outbreak is believed to have weakened in intensity due to the fact most of the population involved have high levels of vaccination. The problem, he said, is that the outbreak is being driven more by crowded living conditions and poverty than under-vaccination.

“In fact, the people who are cases in our outbreak and the communities where these outbreak are occurring are actually vaccinated at higher levels than in other areas of Arkansas,” Haselow said.

Marshall Islanders living in Arkansas are some of the hardest hit by the outbreak, and some of these families live with up to 15 people in a single, three-bedroom home. The crowded conditions are resulting in exposures so high that even the vaccines are no match for the viral load individuals in the outbreak area are up against, he said.

“It makes it so that the intensity and likelihood of exposure is higher,” Haselow said. “Herd immunity assumes people have a representative level of close contacts and intensity of exposure is the same. This community violates these assumptions.”

Next: The third dose debate

Third dose debate

The suggestion that a third dose of MMR may be useful is not new. A 2008 report in Clinical Infectious Diseases suggested that vaccine guidelines for mumps may need revision due to the fact that outbreaks have continued in immunized individuals. Studies have shown that protection against mumps may the weakest of the three vaccines in the MMR series, with subjects in one study testing 95% seropositive for antibodies against measles and 100% against rubella, compared to 74% against mumps after a single dose of the vaccine.

Other research out of Canada has suggested that at least two doses of the vaccine is crucial to stem outbreaks.

Individuals born prior to the initiation of the MMR vaccine in 1957 may have natural immunity. In 1996, the U.S. began recommending two doses of the MMR vaccine for infants, meaning that individuals born between 1967 and 1996 may have only received one dose of the vaccine and not had the chance to develop natural immunity.

Additionally, mumps has become increasingly prevalent in recent years, particularly in 2006 and 2016, due to outbreaks-mostly on college campuses.

But Michael L. Munger, MD, FAAFP, president-elect of the American Academy of Family Physicians echoed the recommendations of the CDC in an interview with Medical Economics.

For anyone who is high risk-college students, those who travel internationally, who work in healthcare, or who were born after 1957 and received only one dose of the MMR vaccine-a second dose would certainly be indicated. However, the decision to give a third dose of the vaccine is dependent on circumstances. Munger, a practicing family physician in Overland Park, Kansas, said he has recommended third doses of MMR to a few patients exposed to college-based outbreaks at the University of Missouri in recent years, but physicians must make the decision on a case-by-case basis considering the specifics of the patient.

As far as other boosters and vaccinations for adults, Munger said PCPs should be reminding patients to get annual influenza vaccinations, pneumococcal vaccines for high-risk patients and those over age 65, Tdap boosters every 10 years and the herpes zoster vaccine for patients over age 60.