Lessons from the Great Mumps Outbreak of 2006

The US mumps outbreak that began early in 2006 was huge both statistically and in terms of the lessons it offered about preventing a recurrence, according to an immunization expert at the Medical College of Wisconsin who regularly speaks and writes on the topic. The average number of mumps cases reported nationwide from 2001-2005 was 265, according to the Centers for Disease Control (CDC), but in 2006 there were 3,200 confirmed cases in 12 states through mid-June, centered in the Midwest.

While reports from local and state health departments and the CDC indicate that the outbreak has been contained, the more than tenfold increase in mumps cases in a single year has rung alarm bells across the country and raised important questions about the effectiveness of current immunization practices. Young adults were the primary victims of the great outbreak, a large percentage of them in high school and college environments.

Mumps virus is spread by coughing and sneezing; common symptoms are fever, headache and swollen salivary glands under the jaw. Mumps can also cause more severe problems including meningitis, hearing loss and swollen testicles that can lead to infertility. Related complications and conditions can lead to death in rare cases, although so far in 2006 there have been no deaths attributed to mumps.

"Mumps is historically a childhood illness," says G. Richard Olds, MD, Chairman of the Department of Medicine and Linda and John Mellowes Professor at the Medical College. "People usually get it when they're relatively small children; six or seven years of age up into adolescence. It is, in the beginning, like many other viral illnesses. People feel crummy and they have muscle aches and pains.

"There isn't a lot that would distinguish mumps from most of the other viruses that we get all the time," says Dr. Olds, who practices at the Froedtert & The Medical College of Wisconsin Internal Medicine Access Clinic. "The unique quality in mumps, which helps distinguish it, is the involvement of the salivary glands. They often get inflamed, and when that happens there's swelling of the cheeks that makes people have that chipmunk-like appearance."

Different Problems in Adults
Iowa, with about 1,900 mumps cases, was hit hardest by the recent outbreak. Wisconsin had 240 confirmed and 345 probable cases. Other states reporting significant numbers of cases were Colorado, Illinois, Iowa, Kansas, Minnesota, Mississippi, Missouri, Nebraska, Pennsylvania and South Dakota.

"When young people get mumps they most often get over it on their own and it generally doesn't cause a great deal of medical problems, says Dr. Olds. "Like many childhood diseases, though, as you get older the disease because more severe." Chicken pox and measles are also much worse in adults than they are in children.

"The problem is that in adult males with mumps, about thirty percent of them will get orchitis, or testicular involvement, and that not only is painful but it can also cause sterility. Fortunately, mumps orchitis is usually unilateral, meaning that it only involves one of the two testes, and the actual incidence of someone becoming sterile as a result of mumps is really quite small, maybe even down to the one percent range.

"That exact number is not very well known because we have really controlled measles, mumps, and German measles, for several decades now, with a live weakened virus vaccine. We historically gave that as one shot, the so-called MMR (measles-mumps-rubella), and that immunized everyone we gave it to against all three of those viruses."

Vaccination "Take" Rate Dropping
When measles-mumps-rubella vaccine was given to children in controlled studies, research data showed more than 95% 'takes', meaning that the vaccine worked. "What we discovered, though, was that in practice when we're using this vaccine the 'take' rate suddenly is dropping," says Dr. Olds. "So we started re-immunizing people against measles-mumps-rubella about ten or fifteen years ago, because we were seeing breakthrough cases of measles in people that we thought were vaccinated.

Many of these cases occurred on college campuses. "When we looked at those cases, many of those young adults said they had gotten the measles vaccine," says Dr. Olds. "So obviously there was some vaccine failure … a fair number, four or five percent, of people who had gotten that one measles-mumps-rubella vaccine were still unprotected and could still get mumps in adulthood.

The response to that was to re-immunize everybody on college campuses against measles, Dr. Olds says. "Some states did the right thing and said 'you know, this is probably also true for mumps and German measles; let's just give them all MMR,' which was the state of Wisconsin's response," he says. "But many states, to save the difference in cost between an MMR and a measles-only vaccine - five or ten dollars - immunized people against measles only." This left people open to the ongoing threats of mumps and rubella.

Using Wisconsin as an example, Dr. Olds noted that even in states that "did the right thing" there are still breakthrough cases of mumps. "The reason that we're having breakthrough cases is interesting," he says. "In about half of those cases they were probably inadequately vaccinated. But about half the cases are occurring in people that claim to have had two measles-mumps-rubella vaccines, so obviously despite even two MMR vaccines some people are still getting mumps. Why could that be?"

Immunization in Practice
Many variables influence the effectiveness of measles-mumps-rubella immunization in real-world vaccination practice, Dr. Olds explains. "In this day and age, where you have to make an appointment to get a shot a couple of weeks in advance and you have to stand in line to see the pediatrician, an interesting phenomenon takes place. Lets say you have a child and that child is sick with some runny nose, some virus, but they have an appointment to get their MMR shot this year.

"Obviously they should wait and reschedule, but they don't do that. They just show up and they get the shot and that virus that they're sick with interferes with the 'take' of the MMR vaccine. That's probably the major reason why people who have actually had two measles-mumps-rubella vaccines are still susceptible, because the circumstances around getting the vaccine are not optimal.

"There might be other explanations, but that's probably the most common explanation. So we haven't been very good at making sure that the measles-mumps-rubella vaccines are given appropriately. In this day and age it may ultimately be more cost-effective to just give three MMR vaccines. So where are we headed in the future? Probably we'll have to give as many measles-mumps-rubella vaccines to the population as is necessary to get a 99% take. Maybe that's three, maybe that's four, maybe it's two with better policing of who gets the shots.

"But as a society we're going to have to be sure that everybody growing up in the United States has enough vaccine so that they don't get measles, mumps, or rubella. We don't want to have young girls not immunized properly against German measles. In their case you don't want them to get German measles when they're pregnant, because even though it's not a serious disease for an adult, it's very detrimental, devastating, to the unborn child."

Dr. Olds says that MMR vaccine supply may be increased in the long term but that's not likely to happen soon, in great part because vaccines in general are not very profitable. "Ultimately, vaccine manufacturers are not in the public health business," he says. "They're in the profit-making business. So unless we begin to mandate more use of the vaccine, in all likelihood the vaccine manufacturers are not going to make any more.

"This does require some public health decisions being made, at least by major colleges and public health officials, to come to the conclusion that maybe we need more measles-mumps-rubella vaccine or better policing of the vaccine. So let's decide that we need to give enough MMR in the future to make sure that we have 99%-plus of our population protected. The problem that we have now is that we're making public health decisions based on the fact that there's a shortage of measles-mumps-rubella vaccine, rather than making good public health decisions."

Dan Ullrich
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.