The Arkansas Department of Health is investigating whether the mumps vaccine is less effective against the type of mumps contracted by hundreds of people during the past three months.
The department counted almost 1,600 confirmed or suspected cases as of Tuesday in the outbreak that was first announced in August, making it the largest outbreak reported to the federal Centers for Disease Control and Prevention this year, a center spokesman said. Northwest Arkansas is most affected, though a handful of cases have been reported in the state's center.
Two doses of the mumps vaccine, which is grouped with measles and rubella in the United States, protect about 88 percent of the people exposed to the virus, according to the CDC. But the type of mumps seen in Arkansas and other recent outbreaks in the country is the most genetically distinct from the type used to make the vaccine, said Dr. Dirk Haselow, state epidemiologist.
Haselow said the strain of the virus making the rounds may have evolved enough to surmount the vaccine, though he added that this hasn't yet been confirmed. "We are 100 percent positive that these vaccines are still helping quite a bit," he said.
Mumps often causes fever, aches and other flu-like symptoms along with the distinctive swollen salivary glands on the side of the face, according to the CDC. The virus can hide for almost a month before producing symptoms, which can last several days. The virus is most commonly spread by contact with an infected person, usually through coughing or sneezing.
The illness in very rare cases can lead to complications such as deafness, inflammation of the brain and its membranes, and swollen testicles in males past puberty.
Arkansas patients have experienced fewer complications than expected, with only one person needing to go to the hospital, Haselow said. He added that it's an example of how the vaccine blunts the disease even if it doesn't entirely block it. It is likely that several thousand people have been exposed but haven't contracted mumps because of the vaccine's protection, he said.
"It's hard to publicize our public health successes -- you don't hear of the guy who avoided a heart attack because he ate well," Haselow said.
The virus has managed to spread despite the department's targeted and mass vaccination clinics in the past weeks and other efforts to wall off the virus from the rest of the population. Nearly all of the school-age children and about 40 percent of adults who caught the disease had been vaccinated, according to the Health Department. Haselow said the case count is still trending upward with no end expected before next year.
Mumps comes in a dozen varieties that have different versions of one gene; each virus holds fewer than 10 genes. The gene in question is involved with countering the body's immune response to the virus, according to a 2012 report in the Journal of Virology by researchers at the U.S. Food and Drug Administration and other institutions.
Outbreaks regularly bounce around the world and country, with Arkansas' outbreak suspected to have started by someone who had been to Iowa, which has experienced its own outbreak with hundreds of cases in the past year or so.
"What we've seen between 30 and 10 years ago is very low levels of mumps, just a few hundred cases in the United States per year," Haselow said. "But starting 10 years ago, there's been a resurgence, and we're seeing higher numbers and larger outbreaks, and more difficult to control outbreaks around the world but also within the United States."
The department also has found some patients who experienced swollen salivary glands for a second time, weeks after their first bout with the disease. This second attack hasn't been described by researchers before, Haselow said.
Haselow isn't the first to question the vaccine's effectiveness when an unusual strain emerges. A 2008 study in the Journal of Infectious Diseases found that vaccinated people could fend off all virus types, while a study the same year in the journal Clinical Infectious Diseases found the length of time since getting the vaccine and other factors seemed to contribute to at least some outbreaks.
The 2012 Journal of Virology study centered on the concept of "immune escape" and found that vaccinated people neutralized all varieties of the virus. Still, "revaccination during adolescence to combat waning immunity" -- a booster shot, essentially -- "might be the most effective measure" to counter outbreaks among vaccinated groups, the researchers concluded.
The Arkansas Department of Health is conducting a study on the effectiveness of a third vaccine dose while it addresses the outbreak, Haselow said. The study won't be finished until the outbreak ends.
The first mumps vaccine was licensed in the United States in 1967. By 2005, mumps rates declined by more than 99 percent because of two-dose vaccinations given to most children, according to the CDC.
Ian Branam, a spokesman for the CDC, wrote in an email that the vaccine protects against the mumps strains now in circulation and directed more detailed questions about the issue to the Arkansas Health Department.
Finding out that people need an additional booster shot in regards to mumps or other diseases wouldn't be unusual, said Dr. Matthew Boulton, professor of epidemiology and preventive medicine at the University of Michigan School of Public Health.
"We went through the same thing in a lot of ways with measles and varicella (chicken pox)," Boulton said, with one vaccine dose recommended until researchers found it still allowed frequent outbreaks. "We try to provide the minimum vaccine doses to provide the maximum protection."
Finding that the mumps vaccine is losing effectiveness "would be rather huge" and would require detailed and compelling evidence, Boulton said.
"If there's any silver lining in all this, I think it will draw more attention to mumps," he added, noting the disease's rare complications can become serious. "In fact, this is an important disease."
Metro on 11/28/2016