Jan 27 2015

Disneyland Measles Outbreak Hubbub

This is an ongoing story that isn’t over yet. As it has been raging for days now, most people have probably heard that there is a big measles outbreak starting in Disneyland in California. There are now 87 confirmed cases of measles, 50 of which can be directly linked to Disneyland. Of the 42 people so far whose vaccination status is known, 34 were unvaccinated, 3 were partially vaccinated, and 5 were fully vaccinated.

Yes, this is caused by those who are not vaccinated

One thing is absolutely certain from these numbers – this outbreak has largely been caused by those who are not vaccinated. As you can see, most of those affected are unvaccinated. The vaccination rate for MMR is about 90% in the US. This means those who are unvaccinated were about 67 times more likely to be infected with measles in this outbreak than those fully vaccinated.

If vaccination rates were higher, then herd immunity could have stopped or severely limited the spread of the disease. That is the point of herd immunity – if enough people are protected then the virus is less likely to find a vulnerable host and continue the spread. The vaccine is about 97% effective in those fully vaccinated, which is why there were a few vaccinated people who contracted the disease.

This is all basic epidemiology. It’s practically just basic math. Yet the anti-vaccine loons and conspiracy theorists manage to make the same mistakes every time an outbreak like this occurs.

An article on NaturalNews writes:

It is entirely possible that a vaccinated person spread the disease to both vaccinated and unvaccinated people, which in and of itself shows the lack of effectiveness of vaccines.

If the vaccine for measles — in the U.S., this vaccine is the combination measles, mumps and rubella (MMR) injection — really did work as claimed, then all the measles cases identified at Disneyland would have been in unvaccinated people. But they weren’t.

This is completely wrong. It is entirely irrelevant who the first case was. When experts say that the outbreak was caused by those who are unvaccinated they are referring of the ability of the virus to spread. The first case is irrelevant. Also, the author makes the common trope of arguing that any cases among the vaccinated show the vaccine does not work “as claimed.” This is demonstrably false, and officials claim the vaccine is 97% effective, not 100%. Actually the data show the vaccine is working exactly as claimed.

They also try to blame the outbreak again on the vaccine itself. The CDC reports that:

An estimated 600,000 to 900,000 persons received KMV in the United States from 1963 to 1967. KMV sensitizes the recipient to measles virus antigens without providing protection.

That’s right – they are still trying to blame measles outbreaks on the almost 50 year old version of the vaccine that is no longer used, and whose effects have likely worn off in the population or been erased by getting an updated vaccine. There is also no evidence that the current outbreak is atypical measles as would result from the killed measles virus vaccine from the 60’s.

The numbers are very clear. This outbreak would not have occurred at all, or would have been much smaller, were it not for the large numbers of unvaccinated people in the population.

Measles is a serious illness

The next chapter in the denial of the implications of the antivaccine movement is to claim that measles is no big deal. Meanwhile, one in four people affected by the current outbreak have had to be hospitalized. Being admitted to the hospital is a pretty good marker that an illness is a “big deal.”

Orac has posted an excellent take down of this claim here.

This is an old strategy. A couple of years ago an Australian anti-vaccine author wrote a book called Melanie’s Marvelous Measles. Sure, two weeks of being miserable with a high fever and rash, and a 30% complication rate, is really marvelous.

Antivaxxers Unphased

You can’t reason someone out of a position they did not reason themselves into (original author unknown, but recently popularized by Ben Goldacre in his book, Bad Science). This is now a core bit of wisdom among critical thinkers. Motivated reasoning can make strong ideological beliefs immune to factual refutation. In fact, exposure to contradictory information may even strengthen the belief by triggering motivated reasoning.

It is therefore of absolutely zero surprise that the antivaccine movement is unmoved by this recent outbreak. The mechanisms of denial, misinformation, and distortion are too well established.


The one good thing to come out of this recent outbreak (and the many other recent outbreaks that have been occurring) is that the media and the public finally seem to be catching on that the anti-vaccine movement is pernicious. Previously contained infectious illnesses are coming back because pockets of vaccine refusal are eroding herd immunity.

Even on Fox News experts are making it perfectly clear that children should be vaccinated or there will be more outbreaks like this one.

Popular culture is reflecting the backlash. An Onion article completely nails it (like only satire can):

I Don’t Vaccinate My Child Because It’s My Right To Decide What Eliminated Diseases Come Roaring Back

I’ll end with the money quote:

The decision to cause a full-blown, multi-state pandemic of a virus that was effectively eliminated from the national population generations ago is my choice alone, and regardless of your personal convictions, that right should never be taken away from a child’s parent. Never.


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