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.

The result was not as quick or dramatic as in the UK, probably because of the public school vaccine mandates, but still pockets of low vaccination rates are already leading to measles and mumps outbreaks on this side of the pond.

The loss of herd immunity affects more than just the children whose parents decided not to vaccinate them. No vaccine is 100% effective, and some children have medical contraindications to vaccinations. These children would also be at risk from those who chose not to vaccinate. Also, the public at large pays the price as previously eradicated diseases make their way back into the population.

Skeptical of Mainstream Beliefs

The LA Times reports that the schools with high rates of vaccine exemptions tend to cluster within affluent schools. They report:

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.

Administrators at the school said the numbers did not surprise them. The nontraditional curriculum, they said, draws well-educated parents who tend to be skeptical of mainstream beliefs.

“They question traditional knowledge and feel empowered to make their own decisions for their families, not deferring to traditional wisdom,” said Assistant Director Kristy Mack-Fett.

There is a great deal of overlap between such attitudes toward vaccines and those of some alternative medicine proponents.  Such attitudes do not reflect true skepticism, which is based upon a respect for logic and evidence. Rather it appears to be a countercultural philosophy – the rejection of ideas not because they lack value but because they represent the mainstream.

This is a knee-jerk “tradition = bad, conventional wisdom = worse” reflex which does not serve these parents or their children well. It is also, I should point out, a logical fallacy – a type of ad hominem reasoning that claims that conventional wisdom is wrong simply because it’s conventional.

Mack-Fett also gives the “empowerment” argument, popular among the promoters of so-called alternative medicine. This is a populist fallacy that counsels the rejection of expert consensus regarding the complexities of science and evidence and tells parents to rely instead on their own knowledge. Of course, this is often being counseled by those who are simultaneously giving gross misinformation.

To be clear, I think that adults should have the right to make health decisions for themselves, and they have a limited right to make decisions for their children (until it conflicts with the state’s duty to protect children from abuse and neglect). Freedom is not the issue. The issue is whether or not it is good practice to pay appropriate consideration to the careful and transparent recommendations from experts or instead to rely upon dubious sources or the vagaries of information on the internet.

Affluent parents, and really most parents today, have been lulled into a false sense of security by the successes of the past. Parents today have never known polio or measles outbreaks, so they downplay their significance. The LA Times again:

“As a parent, I’d rather deal with my kid dealing with measles or mumps and sit with them in a hospital . . . than taking your chances on a shot and having irreversible effects,” said Kim Hart, a mother of two in San Clemente.

I have news for Ms Hart – death is irreversible. Measles can sometimes lead to death. It can also cause other serious and irreversible consequences. What Hart and many parents like her demonstrate is profoundly misplaced fear based upon systematic misinformation. The evidence is clear and overwhelming – the risks from vaccines, while non-zero, is statistically tiny, while the risks from the diseases they prevent is significant and well documented.


As others have already pointed out, what this means is that California is the likely location of future outbreaks of measles and other vaccine-preventable diseases.  We are likely to face at least several years of outbreaks from the damage to the vaccine program that the anti-vaccine movement has already done. If they continue to make inroads into the public consciousness they are likely to do far more damage.

The antivaccine activists deserve unmitigated blame for the death and disease that results from their campaign of fear and misinformation. It is frustrating that as the scientific evidence mounts to show that vaccines are not linked to autism, the antivaccine crowd becomes more and more vociferous. Loudness does not count in science, but it can have an effect in the public arena.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.