A recent article appeared in the Post and Courier detailing the rise of religious exemptions and the threats that they pose to public health. To understand the role that religious exemptions play in herd immunity, one must first look at various vaccine-preventable diseases and the levels of immunity required to keep the disease at bay.

Herd immunity happens when a community is protected against outbreaks because a large portion of the population is immunized. For example, measles and whooping cough both need about 95% of the population to be immunized in order for those who cannot be immunized to be safe from an outbreak. To illustrate how herd immunity works at various levels of immunization, Redditor theotherredmund created the following gif.


The red lines are the disease. Blue dots are those who are unvaccinated and the yellow dots represent people who have immunity. Low vaccination rates mean lots of sick people, but when vaccination rates are high, it’s hard for a disease to really take off.

When people who can vaccinate opt out, it lowers the herd immunity. You might be thinking that 8,074 people isn’t that many, but think about the types of people we’re talking about: school age children. I don’t know about you, but my preschooler and toddler are not exactly known for their sanitation skills. The unvaccinated are likely groups of siblings attending the same school or daycare. Even a handful of families clustered in the same school could wreak havoc on that school’s herd immunity.

So, who does that endanger? Well, sort of everyone, but certain people are more at-risk than others. No vaccine is 100%, and short of having your titers checked (recommended), you don’t know if your vaccines took, so to speak. For most people, the answer is that their vaccines are effective though.

That leaves the at-risk groups. People who have weakened immune systems. These are your individuals undergoing cancer treatments, newborns, pregnant women, the elderly, people who have had organ transplants, people with immune diseases. If you are a parent whose child had a liver transplant as a baby, if you’re the pregnant parent of kindergartener, if your child recently went through chemotherapy, the idea that measles could take off in your school is terrifying. Those individuals will have a significantly harder time fighting off any potential infection.

People who don’t support vaccination like to frame this as a matter of parents’ rights to choose. They exploit the religious exemption to achieve their goal of attending public school without contributing to that school’s herd immunity. The at-risk groups have no choice. They are at the mercy of those around them. We each have an obligation to those around us, and so long as we allow non-medical exemptions to continue, we fail the most vulnerable among us.

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