An extra dose of the combined measles, mumps, and rubella vaccine can help to stop mumps outbreaks, a new study suggests.
The research, published in the New England Journal of Medicine and based on analysis of data from a large mumps outbreak at the University of Iowa in 2015-2016, showed that getting a third dose of MMR vaccine cut the risk of contracting the mumps by 78 percent.
“The thing that this study particularly adds is that a third dose may have a role — at least in outbreak control — for mumps,” said Dr. Saad Omer, a professor of epidemiology and pediatrics at Emory University. Omer, whose work focuses on vaccinations, was not involved in the new study, which was published Wednesday.
Large and protracted mumps epidemics have been happening with increasing frequency in recent years among college students, sports teams, and communities of people who live in close proximity to one another — even though in many cases people who contract the virus have received both recommended doses of the MMR vaccine. The situation has left the public health officials who set U.S. vaccination policy puzzling over what is happening and how to respond.
The panel of experts that advises the Centers for Disease Control and Prevention on vaccinations, the Advisory Committee on Immunization Practices, has set up a working group to investigate the issue and to recommend changes to mumps vaccination policy, if the evidence supports changes. Those recommendations may be brought forward — and voted on — as early as next month, when the ACIP meets again.
The mumps virus, which is transmitted in saliva, causes an illness with many common symptoms — fever, headache, muscle aches. But the virus also infects salivary glands, leading to pronounced swelling on one or both sides of the face. In males infected after puberty, it can also induce swelling of the testicles, a painful condition known as orchitis.
Serious complications of mumps are rare, but can include encephalitis (inflammation of the brain), deafness, and infertility.
Before the mumps vaccine was introduced in the U.S. in 1967, there were upward of 186,000 cases of mumps a year. Annual case counts plummeted after 1977, when ACIP recommended all children receive a dose of MMR vaccine, and fell further still after a second dose was recommended after 1989.
More recently, 6,000 or 7,000 cases in a year is deemed a bad year for mumps. So far this year there have been at least 4,240 cases reported nationally.
In an outbreak at the University of Iowa, 98 percent of the roughly 20,000 students had received two doses of MMR vaccine. Still, 259 students contracted the virus during the outbreak.
In the new study, researchers — from the CDC and the local and state public health departments — went over the medical records of the infected students and saw a pattern. The longer it had been since the students received their second dose of MMR vaccine, the greater their risk of contracting mumps. In fact, students who had received their second shot 13 years — or more — before were nine times more likely to be infected than students who had been vaccinated more recently.
“Collectively these data suggest waning immunity from the second MMR vaccine dose,” said lead author Dr. Cristina Cardemil, a medical epidemiologist in CDC’s division of viral diseases.
One of the senior authors, Dr. Manisha Patel, said the mumps working group is considering these findings and other data as it deliberates on what recommendations to present to ACIP.
One thing that’s not on the table, Patel said, is proposing a delay to children’s second dose of MMR vaccine. The CDC recommends children get their first dose of the vaccine between 12 and 15 months of age and their second between the ages of 4 and 6.
“I will tell you the work group right now is not considering tweaking the one or two dose schedule or moving anything around,” Patel said.
Omer said the group could consider recommending that all teenagers get a third dose of MMR vaccine around the time they get ready to head to college. But he acknowledged the new study doesn’t provide the evidence needed to advocate for an across-the-board third dose recommendation.
Dr. Stanley Plotkin, who played a key role in the development of the rubella vaccine, said he believes a new mumps vaccine is needed. He suggested that a vaccine made with killed or inactivated mumps virus that could be given to teenagers as a booster shot could increase their level of protective antibodies. (The MMR vaccine is made with live but weakened viruses.)
“We can respond like firemen to these outbreaks or we can try to fix the problem prophylactically,” said Plotkin, who consults with pharmaceutical companies and was a consultant to the ACIP’s mumps working group.
Developing a whole new vaccine would cost hundreds of millions of dollars, and Plotkin admitted there’s little enthusiasm for his idea. But he insisted highly publicized mumps outbreaks in fully vaccinated individuals carry a cost as well.
“I’m concerned that the reputation of vaccination is going to suffer if we have these continued outbreaks,” Plotkin said.
Omer didn’t see that as a solution, saying there aren’t new mumps vaccines in the development pipeline, nor are there the financial incentives for industry to produce them.