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Home » Disneyland and measles–some real scientific facts and simple math

Disneyland and measles–some real scientific facts and simple math

Last updated on August 24th, 2019 at 12:20 pm


Unless you’ve been living on an interplanetary spaceship lacking Earth news services, you probably are aware of a serious outbreak of measles at the Happiest Place on Earth, that is, Disneyland (in Anaheim, CA). The park hosts about 40-50 thousand people a day, the bulk of which are children and parents of children, so if there could be a ground zero for a vaccine preventable pathogen outbreak, Disneyland would be the almost perfect place.

According to the California Department of Public Health (as of 30 January 2015), there have been 91 measles cases statewide since the beginning of the new year, with 58 of those cases related (either primarily or through secondary or tertiary contact) to a visit to Disneyland. About a third of those positive for measles are over the age of 20, an unusual statistic (and more on that later).

Some of those infected may have carried the disease outside of the state, but those are being tracked by their home state, so it makes it a bit difficult to get an actual number, but the CDC is monitoring the situation and will give updates weekly. The total number of those who might have contracted measles from Disneyland could be as high as 70-90 individuals.

Facts about measles and the measles vaccines

  • Measles is a serious disease, and can be very dangerous. About 1 out of 20 children with measles gets pneumonia, the most common cause of death from measles in young children. Pneumonia often requires hospitalization, sometimes in a pediatric intensive care unit. Furthermore, about 1 out of 1000 children who get measles will develop encephalitis, a swelling of the brain that can lead to convulsions, and neurodevelopmental disorders. Sadly, about 1-2 out of 1000 children who get measles will die. Let that sink in, because those who claim that measles can be ignored and helps make children healthier are either willfully disingenuous or completely ignorant of real science.
  • The measles vaccine, usually a part of the MMR vaccine (for measlesmumps and rubella) or the MMRV vaccine (MMR plus varicella, also known as chickenpox), successfully prevents measles, a highly contagious respiratory disease caused by a virus.
  • The MMR vaccine is safe. There are no deaths or serious adverse effects associated with the two types of MMR vaccines. Yes, there are people who have dumpster dived through the VAERS database to try to “prove” that the vaccines are dangerous. That’s bad science, and bad statistics.
  • The MMR or MMRV vaccine is not related to autism. This myth is not even worthy of discussion any more, the science, statistics, and the best minds in medicine have published irrefutable evidence that vaccines and autism are not related at all. This myth began with MrAndy Wakefield fraudulently alleging a connection between the MMR vaccine and autism. So unless there’s some gain in perpetrating a lie, this is irrelevant.
  • A package insert is not your source for safety data about a vaccine. There are those who think that the package insert is some gospel from the gods of Big Pharma. It isn’t. The adverse events section, which seems to be the unhealthy obsession of antivaccination cultists, lists only what was reported by patients or physicians without any regards to scientific causality. A clinical trial is not powered in any way to determine adverse events, unless the numbers of events is so large as to provide solid statistics. Observing one event out of 3000 patients may or may not say anything. Observing zero major adverse events in hundreds of thousands of patients, as is done in serious post-marketing research studies, is significant.

Simple math for the vaccine deniers

There are rumors that seem to be perpetuated by the usual suspects in the “let’s lie about vaccines” crowd. One of these pieces of fiction is that those who were vaccinated were more at risk than those who weren’t. That’s just not supported by real evidence.

Only six of those infected by the measles were vaccinated (with one or two doses of MMR or MMRV).

Before we can make any conclusion about what we observed, I want to make some huge caveats about the data:

  1. It annoys me to no end that both “pro-vaccine” and “anti-vaccine” groups are overstating the value of this data. It is 60-90 data points in a non-randomized population. The confidence interval of any data is so huge that it actually borders on being similar to randomly generated data. There is one article that claims that six vaccinated individuals who caught the measles is some sort of indicator of the very tiny rate of ineffectiveness of the vaccine. No it’s not. The data population is too small, too poorly controlled, and too specific to one situation to make any sort of conclusion.
  2. The outbreak is troubling, and I think that it’s the fault of the antivaccination cult. But, there is simply no way to use this small, poorly controlled sample size to place the blame on antivaccine types (and trust me, I know they’re at fault from a gut level, but not from an evidence level.”

All I can tell you is many more unvaccinated individuals contracted measles from Disneyland than vaccinated ones. Using this small, rather useless data group, we can only conclude that your risk of catching measles without the vaccine is substantially higher than those who are vaccinated.

But there’s more math to understand. In medicine, nothing is 100% perfect. NOTHING. The MMR vaccine may be around 95% effective, meaning that 95% of children that receive both doses of MMR will have long-term immunity (if not lifetime immunity). But that doesn’t mean that the vaccine is useless.

In fact, 95% immunity is very powerful. If everyone were vaccinated, then only 5 out of 100 individuals would be susceptible to measles. But measles needs to travel, like most pathogens, by infecting one person, then jumping to another. If those 5 susceptible people are distributed amongst the 95 immune, then the virus really can’t get a foothold. It won’t be be able to “find” the five amongst the herd immunity of the 95.

Of course, if you have one community that is only 50% vaccinated (meaning only 47% have immunity, because of the 95% effectiveness), then there is no herd protection, and the virus can find susceptible people quickly. This may have been one of the underlying reasons for the Disneyland outbreak, but hard to know with such low numbers.

Some advice

Look, I’m all in on vaccines–I reject the misinformation, logical fallacies, and the unscientific nonsense of the antivaccination crowd. Much of the antivaccine stupid arises out of pure fraud, cunning lies, and false balance. Moreover, I don’t get how good, caring parents fall for that ignorant dumbassery, then allow their children to be potentially harmed.

In this “war” for hearts and minds, centering today on the Disneyland measles outbreak, there’s so much nonsense being thrown about:

  • Tired of the battling anecdotes. There’s a science writer whom I totally respect, but they have a huge tendency to use anecdotes to confirm their preconceived beliefs–it’s totally frustrating, and makes me not want to interact with them. Ironically, they constantly criticize the anecdotes of the antivaccination crowd. Anecdotes are anecdotes–just because your wife/husband’s cousins’ hairdresser never caught a disease without vaccines does not make it important data–it isn’t data, it’s just a story.
  • Tired of bad statistics. We can say that the Disneyland outbreak did occur, and it probably spread because of unvaccinated people. But the group is too small for any useful conclusion. I’ll stick with the real science, but I understand how the pro-vaccine forces are desperate for a “victory” so there is a need to overstate what we can actually observe from the Disneyland situation. Oh wait, 95% of people vaccinate. We’ve won the hearts and minds, and I think the crazy vaccine refusers in the wealthy liberal communities of California have got the message. They’ll still buy gluten-free non-GMO organic paleolithic food from the market, but they’ll probably start vaccinating.

Maybe I’m just cranky about this whole story. Vaccines save lives, and there’s just no evidence to the contrary, most people vaccinate, and we’re still arguing about this.

Michael Simpson

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