VaccineIt’s nice when a question can be resolved with objective numbers of unequivocal outcomes. Subjective outcomes give scientists a headache.

In this case we are talking about the effect of vaccine exemption laws on vaccine compliance rates. The question here is not the ethical one, the rights of parents to determine the fate of their children vs the right of the state to protect the health of children and the public health. I think the latter trumps the former, but some disagree.

Regardless of what you feel about the ethical question, we need to know if the laws we pass to achieve our goals actually work, or if they don’t work, or even have unintended consequences. Having an admirable goal is not enough; when you make actual decisions (practice decisions, policy decisions, healthcare decisions for you and for family) you want to know that those decisions are having the desired effect.

We recently had another opportunity to test the effect of vaccine exemption laws, with California law SB 277 making it more difficult for parents to obtain vaccine exemptions. We’ll get to that below.

Vaccine exemption laws

One of the advantages of the US health care system is that in many ways it is 50 statewide systems. This provides the opportunity to experiment – each state is a type of experiment and we can compare the various statewide health care policies on outcomes.

There are a range of policies among the states. All 50 states require some vaccinations for entry into public school. Most offer religious exemptions to vaccines, all but Mississippi and West Virginia. As of 2016, 18 states allow for personal belief or philosophical exemptions (California and Vermont passed laws that remove philosophical exemptions this year). In addition, some states make it more difficult to obtain exemptions – you may have to just check a box on a form, or you may need a notarized note from a doctor, or you may need to be counseled by a doctor about the dangers of vaccine-preventable diseases.

How do these ranges of policies affect vaccine exemptions and therefore the incidence of vaccine-preventable diseases? The answer has consistently been that the more permissive the state regulations, the higher the rate of vaccine exemptions, and the higher the rate of vaccine-preventable illness. The correlation is strong.

For example, a 2006 study looking at state laws and statistics governing vaccine exemptions from 2001-2004 found:

Permitting personal belief exemptions and easily granting exemptions are associated with higher and increasing nonmedical US exemption rates. State policies granting personal belief exemptions and states that easily grant exemptions are associated with increased pertussis incidence.

A 2014 systematic review of state vaccine exemptions concluded:

Findings from 42 studies suggest that exemption rates are increasing and occur in clusters; most exemptors questioned vaccine safety, although some exempted out of convenience. Easier state-level exemption procedures increase exemption rates and both individual and community disease risk.

The easier it is to obtain an exemption the higher the exemption rate, and the higher the incidence of vaccine-preventable diseases like pertussis and measles. Further, private schools have a higher incidence of vaccine refusal than public schools. The exemptions also geographically cluster.

The clustering is important because of herd immunity. If we look only at overall vaccine rates, they usually remain high, enough for herd immunity to prevent outbreaks. But vaccine exemptions cluster, both geographically and in schools, which means there are pockets in which herd immunity is lost. Unsurprisingly, pertussis outbreaks tend to cluster in the same places that vaccine refusal clusters.

It should also be emphasized that the primary reason for vaccine refusal is concerns about vaccine safety. There is no scientific basis for this concern – it is entirely due to a campaign of fearmongering and misinformation on the part of those ideologically opposed to vaccines.

California Law SB277

Comparing different states is useful, and provides a powerful correlation with an obvious causation. However, when one state changes its laws that provides and even stronger source of evidence for the effects of vaccine exemptions laws – because everything is the same except for the law itself.

Largely in response to the Disneyland measles outbreak, California passed a law eliminating personal belief exemptions from the vaccine requirements for public school. The full effects of this law do not kick in until July 1 of this year, but parents were already informed of the upcoming change.

Here come the objective numbers I so love:

Of 551,123 kindergarten children whose schools reported their status, 511,708 (92.9%) had received all required immunizations, an increase from the previous school year of 2.5 percentage points overall, 2.5 percentage points in public schools, and 1.6 percentage points in private schools (Table 1).

Already there has been a 2.5 percent absolute increase in kindergarten children receiving their full vaccination schedule. This is huge from a public health perspective, and will likely have a measurable effect on disease outbreaks in the state.

This also sends a clear message to other states with philosophical exemptions, especially easily-obtained exemptions – this policy does have an effect on public health, which is a direct responsibility of the state.

The net effect of eliminating vaccine exemptions

Requiring vaccines for entry into public schools is a sensible public health policy that is incredibly effective in terms of protecting the public and cost. The cost effectiveness should not be overlooked or minimized at a time when rising healthcare costs literally threaten the quality of our healthcare.

All exemptions increase vaccine noncompliance and increase the risk of outbreaks of vaccine-preventable diseases. The data are clear. This cannot be a point of disagreement when crafting public policy.

There is a reasonable case to be made for not allowing any vaccine exemptions. However, for those states who feel that some exemptions, such as religious exemptions, are appropriate, the data also show they should make those exemptions as limited and difficult to obtain as possible.

I don’t see any justification for philosophical exemptions. They essentially represent allowing a parent to substitute their own ill-informed opinion about the scientific facts for the carefully vetted consensus of scientific opinion. Most parents object because they fear vaccines are not safe, and they are simply and objectively wrong. The benefits of vaccines vastly outweigh the tiny risks. Their children should not suffer, and the public health should not suffer, because of their incorrect beliefs regarding the scientific facts.


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.