Third MMR Dose May Be Useful in Mumps Outbreaks

Laurie Barclay, MD

August 04, 2016

A third dose of measles-mumps-rubella (MMR) vaccine may be considered to help control mumps outbreaks, but proof of efficacy is needed, according to a Centers for Disease Control and Prevention (CDC) report.

Settings in which this control measure might apply are those involving close contact of infected persons with others, sustained transmission despite high two-dose coverage with MMR vaccine, and failure of traditional strategies to limit transmission. However, the Advisory Committee on Immunization Practices has not issued any formal recommendation for or against use of a third MMR dose.

The CDC report, published in the July 29 issue of the Morbidity and Mortality Weekly Report, describes a mumps outbreak confirmed May 1, 2015, at the University of Illinois at Urbana-Champaign. Between April 2015 and May 2016, the Illinois Department of Public Health (IDPH) and the Champaign-Urbana Public Health District (C-UPHD) identified 317 cases.

According to Justin P. Albertson, MS, from the IDPH, and colleagues, "89% of patients with mumps had received at least 2 doses of [MMR] vaccine, and a third dose was recommended as a control measure. The rationale for the recommendation of a third MMR dose included a consideration of seasonal trends and characteristics of the at-risk population. These were weighed against potential drawbacks, which included the potential for vaccine-related side effects, associated costs, and the lack of evidence of the effectiveness of a third MMR dose."

Continued Transmission Despite High Two-Dose Coverage

The index case was a 21-year-old man presenting to the university health center on April 15, 2015, reporting fever and parotitis since April 9. Five additional suspected mumps cases presented in the following 2 weeks; all six patients had received two MMR doses.

A seventh suspected mumps case was confirmed by a positive result on a real-time reverse transcription polymerase chain reaction (rRT-PCR) buccal swab test on May 1, 2015. Epidemiologic linkage of all seven cases confirmed the outbreak.

Standard and droplet precautions for students in healthcare facilities and isolation of sick patients were among the outbreak control measures, as well as vaccination of susceptible close contacts who were not already fully vaccinated. University records revealed more than 97% two-dose MMR vaccination coverage estimated among all students.

However, cases continued to accrue during the summer semester, with 70 cases reported by July 31. On August 4, IDPH, C-UPHD, and the university's McKinley Health Center therefore recommended a third MMR dose for all students and staff born during or after 1957, following CDC guidelines for mumps outbreaks in similar settings.

Among 50,000 individuals targeted for the third dose, 8200 received it on campus from August 6 to 27, an unknown number of students and staff received it off campus before returning to school, and 3300 more were vaccinated during the fall and spring semesters, with no serious vaccine-related adverse events.

Among the identified cases, 32% were rRT-PCR confirmed and 68% were probable. All were epidemiologically connected to the university. Age range was 16 to 55 years (median, 20 years). No patients died; complications included two cases of orchitis and three hospitalizations (one for meningitis treatment, one to rule out meningitis, and one for parotitis pain management). Genotyping in four cases revealed genotype G.

Transmission continued through May 2016 but decreased in the months immediately after August 2015, when the third-dose intervention was implemented. Further research should examine whether this decrease resulted from the recommendation for a third MMR dose.

Third MMR Dose May Be Needed in Similar Outbreaks

Routine recommendations for MMR to prevent mumps are the first dose at age 12 to 15 months (median effectiveness, 78%) and the second at age 4 to 6 years (median effectiveness, 88%). CDC guidelines regarding consideration of a third dose to help control mumps outbreaks include outbreaks among populations with two-dose MMR vaccination coverage of more than 90%, universities and other high-contact settings, sustained transmission for more than 2 weeks, and attack rates of more than 5 cases/1000 population.

This outbreak met CDC guidelines criteria. In addition, it did not follow typical seasonal trends (in Illinois, mumps normally peaks during late winter and spring) because sustained transmission continued into the summer months despite 72% fewer students being on campus. The large number of students returning for the 2015 fall semester would increase opportunities for exposure.

"Both CDC guidelines and factors unique to the outbreak should be carefully considered by public health agencies before issuing a similar recommendation," the report authors conclude. "Additional studies are needed to determine the effectiveness of a third MMR dose as a mumps outbreak control measure in certain populations."

The authors have disclosed no relevant financial relationships.

MMWR Morb Mortal Wkly Rep. 2016;65;731-734. Full text

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