University Mumps Outbreak Prevails Despite High 2-Dose MMR Coverage

The University of Iowa experienced a large mumps outbreak between July 2015 and May 2016, despite a strong university policy for implementing 2-dose measles, mumps, rubella (MMR) vaccine coverage and highly-practiced isolation recommendations after students were diagnosed with the infection. After the outbreak began, the university initiated a third-dose campaign in an attempt to slow the spread of the infection.

“This was an experienced university with a really strong collaboration with state and local health departments,” stated presenting researcher Minesh Shah, MD, MPH, during his oral analysis of the outbreak at the 2017 EIS Annual Conference in Atlanta, Georgia, on April 24, 2017. Dr. Shah and his team evaluated the university’s response to the outbreak along with that of state and local health officials to determine the effectiveness of the community’s third-MMR-dose campaign on the target population (students younger than 25 years of age in the university community).

Dr. Shah began his presentation by noting that 90% of the 301 confirmed cases of mumps in the outbreak were undergraduates, with a median age of 21 years. He added that the level of implementation of isolation guidelines in the university community was “impressive,” particularly in light of the fact that 94% of those diagnosed lived with a roommate or housemate in a housing community other than a dormitory or Greek housing. Students were isolated for a median of six days, and the university promoted the isolation policy by assisting with the logistics of student residence isolation and waiving absences from class.

Most notably, however, 98% of the infected population had already received at least 2 MMR doses at the time that they contracted the illness. “The Johnson County outbreak occurred despite very high 2-dose MMR coverage,” said Dr. Shah, adding that the close adherence to isolation guidelines did not seem to affect the spread of the illness.

When questioned about the accuracy of the reported 98% vaccination rate, he noted that the university requires students to fill out a form at time of enrollment that includes a healthcare-provider certification of receipt of one dose of the MMR vaccine. The form is reviewed by a university healthcare official, and “students cannot register for their next round of courses unless they have two doses,” said Dr. Shah.

After evaluating the response from the university healthcare system and the associated third-dose vaccination campaign which was implemented to bring the outbreak to a halt, the researchers concluded that there was indirect evidence to support the efficacy of the third-dose campaign, but that more research was needed. “We did see decreased cases in targeted age groups [25% vs. 75%] following the third-dose campaign,” Dr. Shah observed. He noted that MMR vaccine effectiveness ranges from 66% to 95% in most cases, which could explain why there was such a high prevalence of infection despite high rates of 2-dose vaccination at the time of the outbreak.

“In a community like a university community, there is a good chance that the infection just overcomes [the odds] and reaches the exposed population,” Dr.Shah said, adding that “about a third” (34%) of students reported direct contact with another student who had mumps. The contact did not, for the most part, occur in the dorms; the majority of the population lived in apartments that are immediately adjacent to the campus and structured very similarly.

Dr. Shah and his team are currently investigating how levels of vaccine effectiveness affected the spread of the outbreak. He noted that in the original study, there did not appear to be a correlation between certain areas of study or intramural sports participation. The group chose not to comment on the absolute necessity of implementing a third-dose requirement based on this study alone.