If 99% of China is vaccinated, why do they have measles outbreaks?

This is a common question from vaccine deniers, and one that does not really surprise me given the lack of math and geography skills many have. The first thing to understand is that it isn’t a 99% rate, in fact 95% of babies in China are currently being vaccinated against measles. Still, that should be enough as the rate for herd immunity is somewhere between 90% and 95%. Keep in mind though, the United States has this rate as well, and still has its own measles outbreaks.

Why is that? Anti-vaxxers tend to cluster together. This is why the large unvaccinated population in Fairfield, Iowa (home of the Maharishi cult and its proud members John Fagan, Jeffrey Smith, and Steven Druker) was able to create just such an outbreak. One of the Maharishi schools went on a little field trip to India, students caught the measles, one ignored advice to stay in India until recovered, then proceeded to infect his hometown and cost taxpayers thousands of dollars to fix their mistake. This same effect has been documented in California as well.

Herd immunity only works at a national scale if those who are not vaccinated are evenly distributed throughout the land. This just does not happen, so now we have to look at populations on a smaller scale. This map of global measles outbreaks explains what is happening. In the United Kingdom, where the entire country was exposed to Andrew Wakefield’s fearmongering via the mass media, herd immunity clearly fell a part on a national scale.


China has more than 1 billion people, but 1 billion is a nice round number so I am just going to round down. With a 95% vaccinated rate, that leaves 50 million unvaccinated. California, the most populous state in the US, only has about 37 million people total. Those 50 million unvaccinated Chinese are not evenly distributed throughout China, if they were herd immunity rates would truly be satisfied. One study in China showed that nearly 12% of parents moving to the city from rural areas had not vaccinated their children.

What is happening is that vaccination coverage varies depending on geographic region, and despite high overall coverage, susceptible pockets of the population still exist. Together China and India are home to 33% of all unvaccinated children on the planet. Other issues existing in China is the number of migrant workers that are not vaccinated, skewing the data even more because they were not counted when born.

Vaccine deniers often struggle with the concept of herd immunity, or even worse will cherry pick the data to make it look like herd immunity doesn’t work. If anything the measles vaccine is strong evidence in favor of herd immunity. Measles is extremely contagious, and 90% of people not immune will catch it from someone who has it in close proximity. So turn the question around on the math deniers. If herd immunity doesn’t work, where are all the outbreaks?

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