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Pockets of Vaccine Noncompliance in California

Posted in Science Based Medicine by Skepdude on April 1, 2009

The LA Times recently published their analysis of data provided them by the state of California and found that there are pockets of high rates of exemption from vaccines among kindergarteners. In the US public schools require that all children receive the recommended vaccines. However, states can allow exemptions for the religious beliefs of the parents.

Over the years anti-vaccine activists have been successful in many states in expanding the rules for exemption. In California, for example, parents may seek excemption if they have “philosophical” objections to vaccines – which means there really isn’t any criteria beyond the parent’s wishes. The anti-vaccine movement has been active not only in pushing for the weakening of vaccine requirements but also in teaching parents how to use the laws to evade vaccination for their children.

The LA Times found that, while state wide the exemption rate was only 2%, exemptions were largely clustered in certain schools. They report:

In all, more than 10,000 kindergartners started school last fall with vaccine exemptions, up from about 8,300 the previous school year. In 1997, when enrollment was higher, the number of exempted kindergartners was 4,318.


At Ocean Charter School in Del Rey, near Marina del Rey, 40% of kindergartners entering school last fall and 58% entering the previous year were exempted from vaccines, the highest rates in the Los Angeles Unified School District.

Herd Immunity

These numbers are concerning because they threaten herd immunity – when about 90% of the population is vaccinated then there are not enough vulnerable hosts to spread an infection efficiently, so outbreaks are uncommon. When vaccination rates drop significantly below 90% then herd immunity is lost and infectious diseases can spread, resulting in outbreaks.

This is not mere theory – it happens. In the UK fears that the MMR vaccine was linked to autism (even after the original research by Andrew Wakefield was exposed as wrong, subject to undisclosed conflicts of interest, and maybe even fraudulent, and later evidence confidently showed no link between MMR and autism), led to a precipitous drop in the rates of MMR compliance. The UK does not mandate vaccine for entry into public schools, so they lacked the buffer (for what it’s worth) that exists in the US. As a result there was, and continues to be, a resurgence of previously controlled diseases, like measles.

The later scare that the mercury-based preservative thimerosal could be linked to autism has had a similar effect, and such fears rapidly spread to the US.  This link too has been shown to be false, and in any case thimerosal was removed from the childhood vaccine schedule by 2002, but the this has not stopped the anti-vaccine movement from spreading unwarranted fear.


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