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Home » Yes, vaccine herd immunity works – scientific evidence supports this fact

Yes, vaccine herd immunity works – scientific evidence supports this fact

This piece is a summary of Herd Immunity and Immunization Policy: The Importance of Accuracy, published in v. 94 of the Oregon Law Review.

As a bit of background, in an article that was published in the Oregon Law Review in 2014, authors Mary Holland and Chase E Zachary claimed that school immunization mandates are inappropriate because they reject the concept that herd immunity works.

This article will explain why Holland and Zachary’s analysis or immunization mandates and herd effect is simply incorrect. And let’s be clear – there is a legitimate debate about whether school immunization mandates are appropriate, policy-wise, as a response to non-vaccination.

Unlike vaccine science, the appropriate policy to handle non-immunization is not agreed upon, and the data on what is the right way to get people to vaccinate is anything but clear (though some things are clear – for example, harder to get exemptions lead to higher vaccination rates). But the debate needs to be premised on accurate facts – not on misuse of legal terms and incorrect scientific data. Holland and Zachary’s article does not provide that.

herd immunity
Herd immunity graphically explained.

The criticism of Holland and Zachary’s conclusions are focused on three major points:

1. Duty to protect children

First, it highlighted that Holland and Zachary confuse society’s duty to children – embodied in the idea of parens patriae, the state as the guardian of the vulnerable – with the duty of care we use in torts. The duty of care in torts is a threshold requirement – it explains which kinds of claims will get their day in civil courts and have a chance to be compensated, and which will not.

That’s not what society’s duty to children is about – it’s not a barrier to suing, instead it’s a moral responsibility of the state to protect its more vulnerable members – in this case, children.

Holland and Zachary suggest that the duty to children “is suspect because there is no clear analog in common law criminal or tort systems” – but parens patriae is neither new nor controversial. The term simply has a different meaning that the duty as used in the other contexts and confusing the two is a legal error.

Further, in another section, when discussing a duty to protect children – this time of the family, not society – Holland and Zachary seem to see the family as having a duty to protect children only from vaccine injuries (p. 37). In other words, they completely ignore the family’s duty to protect children from the risks of diseases – a risk that, the scientific consensus highlights, is much higher than the risk of serious vaccine injury – an extremely rare occurrence.

herd immunity

2. Herd immunity is unachievable.

Second, the authors suggest herd immunity is unachievable. To do that, they define herd immunity as “the complete removal of a disease from society” (p. 8). But that is not how herd immunity is defined in the very paper they rely on, and it is not how the term is used from a public health perspective.

In their claim that herd immunity is unachievable, they also ignore abundant data supporting it. That data includes the dramatic decline of vaccine-preventable diseases after the introduction of the vaccine – studies showing that it’s safer to be unvaccinated in a community with high immunization rates than vaccinated in a community with low immunization rates. Furthermore, studies showing that vaccinating children has a general protective effect on adults and the community, as well. In other words, there is abundant evidence that herd immunity from vaccines works.

In part, the claim that herd immunity does not work relies on a claim that vaccines only offer short duration of immunity, a claim raised by many anti-vaccine sites – but which is only true for some vaccines (pdf ).

The article analyzes the two examples provided by Holland and Zachary to show herd immunity does not work – the measles and chickenpox vaccines – and shows how they actually support herd immunity.

3. Herd immunity may be undermined by individual choices

Finally, the article highlights an analytical flaw in Holland and Zachary–individual choices may lead people not to vaccinate in ways that will undermine herd immunity, and end with an immunization rate below the threshold needed to achieve herd immunity. If taken seriously, the conclusion is that under their analysis voluntary compliance alone will not achieve herd immunity, and will contribute to outbreaks.

A quick look at the example they highlight – Europe, where school mandates do not exist – demonstrates this point. Without school immunization requirements, Europe has pockets where rates of immunization with MMR are low. As a result, Europe has seen high rates of measles, much higher than the United States – with deaths, encephalitis, and many hospitalizations (pdf).

If anything, the European example highlights the usefulness of school immunization requirements – which is why some countries, such as Germany, Italy, and France are either considering mandatory vaccinations or have already implemented them.

herd immunity
A herd of elephants representing herd immunity. Photo by Harshil Gudka on Unsplash


In short, while there is room for a legitimate debate about the desirability of school immunization requirements, a claim against them that is based on misuse of legal concepts, mischaracterization of the science, and a flawed analytical structure cannot stand. The article in question does not advance the debate about the appropriate policy in relation to non-immunization.


This article was published in April 2015 by Professor Dorit Rubinstein Reiss, Professor of Law at the University of California Hastings College of the Law (San Francisco, CA). Because of the recent measles epidemic, the anti-vaccine tropes regarding herd immunity have become more prevalent. Thus, it was important to update and republish this article as a reference about how herd immunity works.

Dorit Rubinstein Reiss

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