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This past week, the National Hockey League was rocked with over a dozen cases of what is now a rare viral illness, the mumps. The virus, which used to infect about 186,000 Americans each year, has dwindled with only a few occasional outbreaks occurring annually thanks to vaccination. Yet, as the NHL has now learned, when the disease does enter a susceptible community, it can affect anyone, including superstars like Sidney Crosby.

The virus causing mumps is a member of the Paramyxoviridae family and has been known since the 1930s. Over the decades, how infection occurs has been elucidated. The process begins after contact with an infected person leading to introduction of the virus into the respiratory tract. In about a third to half of exposed individuals, there are no symptoms other than a mild respiratory illness. For the majority, however, the virus incubates for between two to four weeks as it migrates to the parotoid (salivary) glands. Once there, it causes significant swelling leading to the classical appearance of ‘chipmunk cheeks.’

The illness traditionally lasts for only a week and then resolves without complications. However, between 1 and 10 percent of infected individuals may experience neurological symptoms including meningitis. In up to a quarter of men, the problems may worsen as the virus travels to the testicles leading to a condition known as orchitis. In a very small number of cases, other problems may occur including polio-like paralysis.

Until 1977, the virus spread rapidly across the United States. At that time, the measles, mumps, and rubella vaccine (MMR) was introduced and the numbers dropped significantly. However, the vaccine wasn’t entirely perfect and failures were identified leaving the potential for outbreaks and small scale epidemics.

In children, the efficacy of one dose of vaccine was found to be as high as 96 percent but could be as low as 66 percent. This led to the introduction in the 1990s of a second dose (a booster shot) to bump up the effect. This in turn helped to bring the efficacy to 99 percent. Unfortunately, the actual administration of the two-doses was not universally performed leaving some populations susceptible to the virus.

As public health officials recognized the need for a second dose in children, other researchers were looking at the need in adults. In 2007, a study revealed those who didn’t get the booster were more likely to have a waning response to the virus, meaning as they grew older they would become more susceptible to infection. This in turn could mean an outbreak could potentially occur. As a result, the recommendation for a booster shot for everyone became the norm.

Yet there was a caveat. In a study conducted during one particular mumps outbreak in 2006, researchers realized that there was a link between the length of time between the first vaccine dose and the booster. This potentially could lead to a gap in protection in which those receiving a booster may still not be able to fight off a natural infection. In light of this information, the concept of a third dose was suggested and tested. The results showed an improvement in the overall coverage as well as improved immune function against the virus. However, the results were not entirely conclusive and required further study.

While the vaccine debate continues, the fears of a slow but steady resurgence of mumps have become realized. The combination of a lack of natural infection and either no- or under- vaccination has allowed the virus to return in a number of countries including the United States. Though the numbers are small – only a few dozen each year – for public health officials, this presents a rather disturbing trend although it may have been hard to convey to the public.

Now it seems the NHL has offered a possible route to public health remedy. The outbreak has offered a perfect demonstration of how rapid this virus can spread. The hockey environment is perfect for the transmission of mumps; bodily fluids such as saliva and nasal secretions are constantly being shared inadvertently through droplets. In addition, the immunological makeup of the players and staff is such that the overall vaccine coverage against the virus is less than optimal. Some may have never been vaccinated. Others may have received the vaccine but lacked the proper immunity to fight off the illness. Although the booster shots are now being given en masse the outbreak most likely will continue for another few weeks to months.

Although this outbreak has gained significant media attention it will end with little to no long term consequences. Most or even all of those affected will recover fully and return to playing without any concern. Yet, there is a takeaway message: we can never count out a pathogen, even if there is a vaccine against it. Whether mumps, measles, polio or pertussis these viruses can easily find non-vaccinated or under-vaccinated populations and spread like wildfire. There needs to be a stronger adherence to proper vaccination, especially when recommendations change, and the development of proper immunity. Only in this way can we one day look at these viruses as relics of history – like smallpox – rather than harbingers of future health concern.

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