Majority of mumps cases are among vaccinated, study finds

New research from CDC, published in the December issue of Pediatrics, shows that the virus that causes mumps continues to circulate in the United States, primarily infecting people vaccinated against it, including children.

The study found that one-third of the reported U.S. mumps cases from 2007 to 2019 occurred in children and adolescents. As many as 94% of those who contracted the respiratory illness had been vaccinated against the disease.

Researchers said possible contributing factors for reduced immunity against mumps include waning immunity; a lack of prior exposure to the virus; and the circulation of genotypes not contained by the measles, mumps, and rubella (MMR) vaccine.

Nearly 91% of the U.S. population has had at least one dose of the two-dose MMR vaccine, which is administered between 12 months and 6 years and is 88% effective against the disease.

In a companion editorial, Charles Grose, MD, from the Department of Pediatrics at the University of Iowa, writes that it might be time to administer a third dose of the MMR vaccine, preferably one that does not contain the genotype A strain, which no longer circulates in the United States.

“There are other live attenuated mumps vaccines being used elsewhere in the world. One is based on the Urabe strain from Japan (genotype B)[,] and another called the Zagreb strain was derived from a Russian strain (Leningrad strain) [… S]hould we consider a third immunization with the Urabe strain or the Zagreb strain of the mumps vaccine? That strategy presumably would broaden the neutralization antibody response in vaccine recipients,” he writes.