And here we go again. An outbreak of a vaccine preventable disease is used by the anti-vaccine crowd to indict all vaccines. Recently, the Harvard mumps outbreak has made the news after about 41 students contracted the disease. And myths arise.
Since most of those who caught the disease were vaccinated with the MMR vaccine, which protects against measles, mumps, and rubella, the anti-vaccine interwebs are jumping up and down pointing at the pro-science people and saying, “neener neener, vaccines don’t work.” Yeah, they’re that immature. And they are absolutely wrong.
Let’s take a look at the whole story, including some very simple math, which even science deniers should understand. Then we can thoroughly debunk the tropes pushed by the vaccine deniers. This should be fun.
All about mumps
Mumps is caused by the mumps virus, known as Rubalavirus. It is a highly contagious disease that is transmitted through mucous from sneezing, coughing or passive touching. College classrooms and dormitories are perfect vehicles for the transmission of these highly contagious diseases. Like Harvard University.
Mumps is best known for the puffy cheeks and swollen jaws that result from inflamed salivary glands. The mumps look was quite prevalent prior to the advent of vaccines, so most people today have never experienced contracting the disease or seeing others with it.
Aside from the swollen facial appearance, other common symptoms of mumps include fever, headache, muscle aches, tiredness, and loss of appetite. Generally, the symptoms are very similar to the flu, except for the swollen salivary glands.
Symptoms usually appear 16-18 days after infection, but it can be shorter or longer than that. Some cases of the disease are so mild, that the individual doesn’t even know they have the disease, but still can transmit the disease to others. Most people with mumps recover completely in a few weeks.
Now, this sounds perfectly benign. Except that it isn’t.
Mumps has some very serious complications, especially for adults. Here are some:
- inflammation of the testicles (orchitis) in males who have reached puberty. This happens in about 15-40% of men who have reached puberty and contracted the disease. This condition rarely leads to fertility problems, but it is a risk of catching the disease as an adult male.
- inflammation of the brain (encephalitis) is rare, but about 1% of cases are fatal.
- increased risk of spontaneous abortion of the fetus in pregnant women who contract the disease.
- inflammation of the tissue covering the brain and spinal cord (meningitis) occur in about 10% of cases.
- inflammation of the ovaries (oophoritis) and/or breasts (mastitis) in females who have reached puberty arise in about 5% of cases.
- profound deafness is very rare consequence of mumps.
Yes, the risk of most of the more serious issues are very small indeed. But, it is still there. And, that risk approaches zero after vaccination against mumps.
Becauseecause of widespread vaccination, mumps is an extremely rare disease, and the complications are hardly ever seen these days.
Harvard mumps outbreak – what happened?
As I mentioned above, mumps is very contagious. And places where people are in close contact with each other, like in the dorms, dining rooms, clubs and classrooms of Harvard University, the disease will pass quickly from one individual to another. Colleges are like a petri dish for pathogenic diseases.
The bigger point is, if all of these students were vaccinated against the mumps, why would there be an outbreak? Because, every single pro-science vaccine supporter says, “vaccines are perfect.” Well, we don’t say that nonsense.
The simple answer to “why was there an outbreak” is nothing in medicine is “perfect,” and no one claims that vaccines are perfect. According to the CDC, the mumps component of the MMR vaccine is around 88% effective after the standard two vaccine series.
And like other vaccines such as pertussis, there is evidence that the mumps vaccine also has shown some waning immunity. It’s probably been 10-15 years since those students had their last MMR vaccine, so it’s possible that effectiveness dropped by a few percentage points.
In the 1960s, before widespread vaccination of the diseases, there were around 186,000 cases of mumps per year. At that level, even rare complications would be relatively common.
Recently, in the USA, we’ve seen around 200-2000 cases of mumps per year, some because of unvaccinated individuals, and some from the waning immunity of the vaccine.
Now, those who love the Nirvana logical fallacy, that is, if it isn’t perfect it’s junk, will say that the mumps vaccine is worthless. And since the 41 students at Harvard who contracted the disease were all presumably vaccinated (Harvard requires the vaccine before enrolling), so that means the vaccine is even more worthless.
Let’s look at this.
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The simple math
Harvard University has around 21,000 undergraduate and graduate students on campus. It has also around 5,000 academic staff, 14,000 post-graduates, and thousands of more staff.
But let’s just stick with students, because that’s all that’s necessary. The 41 cases represent about 0.2% of the students at Harvard. That’s tiny.
If we use the national estimate that mumps vaccine is around 88% effective, then we actually would predict that 2520 students would have contracted the disease, since it’s so contagious, it probably would spread that fast.
In other words, just using simple math, vaccines reduced the predicted disease incidence of 2520 to around 41 – that’s a reduction of around 98% risk.
Now, I’ve oversimplified this analysis by a lot of factors, including how much contact there is between all of the infected individuals, directly and indirectly. But if we assume that a person is infectious for 20 days before symptoms appear, it is reasonable to assume that there’s a lot of contact between individuals. Remember, I’ve also ignored the potential waning immunity which might make the predicted incidence of the disease much much higher.
And even more than that, the numbers point to one unassailable fact – herd immunity undoubtedly blocked transmission from going further than it did.
In other words, the Harvard mumps outbreak doesn’t tell us that vaccines don’t work. It tell us how much they do work, even when they’re not perfect. Seriously, it’s really simple math.
That being said, like with all vaccines, especially pertussis, science needs to figure out how to improve them. Maybe we need to add another booster shot. Maybe we need to look at improving the immunization effect of the vaccine. Or something.
The problem with mumps is that there is a perception (not based on reality) that it’s a minor disease, and we shouldn’t invest much into improving it. I don’t agree with that thinking, but vaccine research is focused on the “disease of the week,” instead of examining the current ones.
Nevertheless, the mumps vaccine was highly effective in preventing a larger outbreak at Harvard. And that’s an important consideration that’s lost on the anti-vaccine activists. But evidence and science isn’t high on their list.
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Key citations
- Barskey AE, Glasser JW, LeBaron CW. Mumps resurgences in the United States: A historical perspective on unexpected elements. Vaccine. 2009 Oct 19;27(44):6186-95. doi: 10.1016/j.vaccine.2009.06.109. Review. PubMed PMID: 19815120.
- Davis NF, McGuire BB, Mahon JA, Smyth AE, O’Malley KJ, Fitzpatrick JM. The increasing incidence of mumps orchitis: a comprehensive review. BJU Int. 2010 Apr;105(8):1060-5. doi: 10.1111/j.1464-410X.2009.09148.x. Epub 2010 Jan 11. Review. PubMed PMID: 20070300.
- Dayan GH, Quinlisk MP, Parker AA, Barskey AE, Harris ML, Schwartz JM, Hunt K, Finley CG, Leschinsky DP, O’Keefe AL, Clayton J, Kightlinger LK, Dietle EG, Berg J, Kenyon CL, Goldstein ST, Stokley SK, Redd SB, Rota PA, Rota J, Bi D, Roush SW, Bridges CB, Santibanez TA, Parashar U, Bellini WJ, Seward JF. Recent resurgence of mumps in the United States. N Engl J Med. 2008 Apr 10;358(15):1580-9. doi: 10.1056/NEJMoa0706589. PubMed PMID: 18403766.
- Hviid A, Rubin S, Mühlemann K. Mumps. Lancet. 2008 Mar 15;371(9616):932-44. doi: 10.1016/S0140-6736(08)60419-5. Review. PubMed PMID: 18342688.
- Senanayake SN. Mumps: a resurgent disease with protean manifestations. Med J Aust. 2008 Oct 20;189(8):456-9. Review. PubMed PMID: 18928441.
