When you think of the mumps, you probably think of the MMR vaccine. You probably don’t think of an outbreak, which isn’t actually all that uncommon. Last year, there were 5,311 reported cases, according to the CDC, mostly clustered in college areas. This year has started off with a bang: January saw 495 cases in 27 states. It gets worse: As of February 7, the Washington State health department had reported 367 cases alone. Most of those, according to ABC News, are in school-age children. Of those kids, 87% were vaccinated.
Mumps infection in vaccinated children? Cue the anti-vax crusaders. There’s no such thing as herd immunity, screams Vaccine Impact about the 2016 Harvard mumps outbreak, and the vaccine is ineffective, they say. Anti-vax crusader and natural health shill Mercola claims there’s no such thing as vaccine-induced herd immunity, and the mumps outbreaks prove it. The Vaccine Reaction ballyhoos the lawsuit brought against Merck by two of the company’s scientists, who allege Merck falsified data about the MMR vaccine’s effectiveness against mumps, claiming it had 95% efficacy in preventing the disease. Since the CDC itself claims the two-dose series of vaccine has an average 88% efficacy rate (ranging from 66% to 95%), this makes no sense. But let us soldier onward.
According to the CDC, mumps used to be a standard disease of childhood. It causes “pain, tenderness, and swelling” of the parotid, or salivary, glands. A fever may last for three to four days, and there’s often an accompanying headache. Sound benign? It’s not.
Complications include swelling of the testicles (12% to 66% of post-pubescent males pre-vaccine), which can cause sterility. It can also cause encephalitis (1 in 6,000 to a scary 1 in 300 cases pre-vaccine), meningitis, and mastitis (affecting a whopping 31% of women in one outbreak. Ovarian swelling was found in 5% of cases. Pre-vax, temporary deafness occurred in 4.1% of infected military personnel, with permanent, one-sided deafness happening in 1 in 20,000 instances. From 1966 to 1971, 2 deaths per 10,000 cases were reported in the United States. These were caused by encephalitis. In 1964, around 212,000 people in the United States contracted mumps. The vaccine was introduced in 1967. A year later, in 1968, only 152,000 cases were reported. In 1985, the CDC only received notice of 2,982.
So the vaccine works. And this disease isn’t exactly a benign childhood illness, especially when it’s your kid’s testicles swollen up like a grapefruit, and you’re panicking about the possibility of grandchildren.
— André Picard (@picardonhealth) February 22, 2017
The mumps outbreak in vaccinated people doesn’t prove the vaccine doesn’t work. It proves what scientists already know: The vaccine is only 88% effective. In some people, the vaccine simply doesn’t prevent sickness. And like all vaccines, the efficacy of the mumps vax can wane over time.
In fact, Consumer Reports quotes Dr, William Schaffner, MD, as saying that “after 10 to 15 years, effectiveness of the mumps vaccine may diminish.” So close quarters, like college dorms, provide fertile ground for viral transmission.
Scientists know all this stuff, and they also know that the mumps vaccine isn’t the greatest — the measles vaccine, for example, is something like 99% effective with two doses. So no shock from public health peeps that mumps will crop up from time to time. It usually comes from overseas, where vax rates are lower than in the United States.
And paradoxically to the anti-vaxxers, mumps outbreaks actually prove that herd immunity works. Compare the pre-vax and post-vax outbreak numbers I mentioned earlier. See a difference? 212,000 cases in 1964, 5,311 cases in 2016, which was a “bad” year for mumps. Herd immunity means that once a certain vaccination threshold is reached (and yes, Mr. Mercola, it works the same in vaxed communities as in those who achieve immunity through good ol’ fashioned illness) even people who aren’t vaccinated are less likely to get sick. Because these mumps outbreaks do burn out, rather than leaving a flaming swath of infection across the country, they actually prove herd immunity.
— Bryce Hoye (@brycehoye) February 13, 2017
Outbreaks now are usually confined to one space — often a college, where kids swapping spit in various salacious ways may contribute to its spread. Last year, Harvard saw 40 cases of mumps, according to Wired — out of an undergrad population of 6,600. That’s vaccine efficacy if I ever saw it.
Moreover, the cases of mumps among vaccinated populations are less likely to result in complications. So even if you get sick, you get less sick. In recent outbreaks, the CDC reported that testicular swelling rates are down to 3.3% to 10% of cases — far from the 12% to 66% of yore. Ovarian inflammation is down to 1%. Most notably, the CDC has shown that “incidents of meningitis, encephalitis, pancreatitis, and deafness have all been less than 1%.” No one has died of mumps in recent memory. The vaccine works.
— Molly Shen (@MollyShenKOMO) February 2, 2017
So while we wish we had a better mumps vaccine, we don’t have much to fear from it. In fact, Wired noted the Mayo Clinic’s Vaccine Research Group tried to get a grant to see why the mumps vax wasn’t more effective and failed, because it wasn’t that much of a public heath priority. The current vaccine, at 88% effective, is already enough to protect most of us.
And as for those who get the virus, well, they don’t get that sick, because they’ve been vaccinated. From a rite-of-passage disease to a headline-worthy event, mumps could be considered a vaccine success story. Anti-vaxxers can scoff all they want. The vaccine works 88% of the time. That’s enough to prevent widespread outbreaks and confer enough immunity to prevent dangerous complications, which is why we have the vaccine in the first place.