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Predicting US measles outbreak – vaccine uptake and international travel

The locations of the current US measles outbreak (or epidemic) was predicted by researchers in an article recently published in Lancet Infectious Diseases. The amazingly prescient predictions were not based on magic, but on a scientific analysis of two factors – the vaccination rate and international travel tendencies by county in the United States.

And the statistical website, Five Thirty-Eight, took the predictions and listed out what happened during this US measles outbreak. The predictions were spot on.

Time to look at this study and its predicted results.


US measles outbreak
Obligatory cute kitten picture. It has nothing to do with vaccines. Photo by Jari Hytönen on Unsplash

Predicting the 2019 US measles outbreak

Researchers from the USA, Australia, and Canada developed a quantitative model that identifies USA counties that are at the highest risk of a measles outbreak in 2019. They developed this model, at a county level, that incorporates five factors:

  1. International air travel to the destination county.
  2. Non-medical exemption (NME) rates in the country. The researchers attempted to use county-level NME rates – if that data was unavailable, they used state-level NME rates or estimated vaccination rates.
  3. Kindergarten vaccination rates. 
  4. The population of the county.
  5. And the incidence rate of measles outbreaks at the international travel origin point.

The researchers produced this map which showed the 25 US counties with the highest relative risk for a measles outbreak in 2019.

US measles outbreak
Credit: The Lancet

For those of us who follow this US measles outbreak and where the anti-vaccine zealots seem to be centered, this map is not surprising at all. In fact, many of us could have predicted the risk for most of these counties with a back of the napkin calculation. But science is always better with real data instead of anecdotes and bad research

How does this compare to observed numbers?

According to an article in FiveThirtyEight, the predictions were frighteningly accurate.

US measles outbreak
Credit: The data was derived from the New York Times, Washington Post, and the Centers for Disease Control and Prevention.

They correctly predicted 14 out of 25 US counties with the highest risk in 2019 for measles actually having measles cases. And remember, 2019 is only half done, so these predictions could be much more accurate when we revisit them early next year.

California is attempting to deal with non-medical exemptions by regulating them more closely with SB276, legislation that is wending its way through the California legislature despite hyperemotional pseudoscience and lies from the anti-vaxxers. 

Actually, this study could even be better. The Centers for Disease Control and Prevention (CDC) actually has data that details confirmed measles cases by county and zip code, which could help researchers make more accurate predictions of measles outbreaks. 

For example, the Lancet article states that Los Angeles County, California, has a high risk of a measles outbreak, which happened. However, Los Angeles is a very large county with over 10 million inhabitants, larger than 41 US states (and many countries). What I would want to know if the risk for measles is spread equally across the county, which I sincerely doubt? Or is the risk centered in wealthier white zip codes, which I assume is the case?

Sahotra Sarkar, a professor of philosophy and integrative biology at the University of Texas at Austin, one of the lead authors on this study, also commented that they could refine their data to the zip code level with this CDC information. We’re not sure why the CDC hasn’t released it, but I’m assuming it will be in a forthcoming paper that will discuss the 2019 US measles outbreak. Or more clearly, measles epidemic.

FiveThirtyEight made some key points about these findings:

There are basically two things you need to make a measles outbreak in the U.S. The first is a local community with a low vaccination rate. Although 91 percent of Americans nationally are vaccinated against measles, isolated pockets can have much lower rates — 70 percent, 50 percent, or even less. Insular communities connected around shared culture, religion or a single school provide a place where measles can incubate and spread, said Peter Hotez, professor of pediatrics and molecular virology at Baylor University. If a measles outbreak is a fire, you can think of this as the tinder.

Since I don’t have to be as diplomatic as Dr. Hotez, let me be blunt – anti-vaccine activists are putting our children and our citizens at risk of a dangerous, deadly disease. This data shows us where these vaccine deniers are located, and it is troubling.

One more thing – from a political point-of-view, most of these counties are “liberal” leaning. I’m disgusted that my fellow liberals might be anti-science pro-disease dimwits. Of course, I know that the anti-vaccine religion has members from the far left and the right, so it’s not just a liberal thing. But I expect more with regards to science from liberals.

Vaccines cause adults. And save lives. And prevent measles.


Michael Simpson
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