Most children with mumps are vaccinated, study finds

A study found that, from 2007 through 2019, one-third of reported mumps cases in the United States occurred among children and adolescents, most of whom were vaccinated.

The study was conducted by researchers at the CDC and was published in Pediatrics.

CDC epidemiologist Mariel Marlow, PhD, MPH, told Healio in an interview that high vaccination coverage has maintained control of mumps in the U.S.

“However, there has been a rise in cases among vaccinated children and adolescents,” Marlow said.

Marlow and colleagues noted several possible reasons for this, including a waning of vaccine-induced immunity and potential mismatches between the vaccine and circulating virus strains.

“Increasing incidence with increasing age, correlating with likely increasing time since vaccination, supports the hypothesis of potential waning immunity against mumps infection following vaccination,” they wrote. “Some epidemiologic or modeling studies have suggested that vaccine-derived immune protection against mumps wanes by early adulthood. However, the results presented in this study show vaccinated individuals can become susceptible sooner than young adulthood.”

For the study, the researchers assessed all reported mumps cases between 2007 and 2019, and examined factors including age, state of residence, vaccination status and whether the case was associated with an outbreak.

“In addition, we analyzed pediatric mumps cases during the most recent resurgence between 2015 and 2019, including sex, age, race/ethnicity, state of residence, import status, whether the case was associated with an outbreak, vaccination status, parotitis, complications, hospitalization, and death,” Marlow said.

During the 2007 to 2019 period, researchers found that a total of 9,172 pediatric mumps cases were reported, accounting for a median of 32% of all cases reported each year (range: 13%-59%). Between 81% and 94% of these cases occurred among children who had received one or more doses of the MMR vaccine, Marlow and colleagues reported.

“Before 2006, large outbreaks of mumps among people who were fully vaccinated were not common, including among vaccinated children,” Marlow said.

In an accompanying editorial, Charles Grose, MD, a professor of pediatric infectious diseases at the University of Iowa Carver College of Medicine, traced the history of the mumps virus and noted that, following the mumps vaccine’s creation, “cases dropped precipitously, but the mumps vaccine was never as effective as the measles vaccine.”

“A recent Cochrane analysis of mumps vaccination in multiple countries stated that one dose of mumps vaccine was 72% effective, and two doses of mumps vaccine were 86% effective,” Grose wrote. “Several investigators have concluded that mumps likely remains endemic in the United States.”

What will be most important for providers, Marlow said, is to suspect mumps in children with symptoms like pain, tenderness and swelling in salivatory glands, along with fever, headache, muscle aches, tiredness or loss of appetite.

“As mumps has continued to circulate during the pandemic, both in the U.S. and abroad, we can expect to continue to see cases and outbreaks of mumps nationally,” Marlow said. “We also know that disruptions from the COVID-19 pandemic resulted in many children missing well-child visits and routinely recommended vaccines, including MMR, which could contribute to a future increase in cases or outbreaks, as people who are unvaccinated are at a higher risk for mumps and mumps complications. Vaccination with MMR is the best way to protect against mumps.”

Reference:

Grose C, et al. Pediatrics. 2021;doi:10.1542/peds.2021-052761.