Here's Why Rational People Skip Vaccines Even When They Trust Science

When outbreaks of vaccine-preventable diseases such as measles occur despite highly effective vaccines being available, it's easy to conclude that parents who don't vaccinate their children are misguided, selfish or have fallen prey to misinformation.

In our view, it involves game theory, a mathematical framework that helps explain how reasonable people can make choices that collectively lead to outcomes that endanger them.

Game theory reveals that vaccine hesitancy is not a moral failure, but simply the predictable outcome of a system in which individual and collective incentives aren't properly aligned.

Game theory meets vaccines

Game theory examines how people make decisions when their outcomes depend on what others choose. In his research on the topic, Nobel Prize-winning mathematician John Nash, portrayed in the movie A Beautiful Mind, showed that in many situations, individually rational choices don't automatically create the best outcome for everyone.

Vaccination decisions perfectly illustrate this principle. When a parent decides whether to vaccinate their child against measles, for instance, they weigh the small risk of vaccine side effects against the risks posed by the disease. But here's the crucial insight: The risk of disease depends on what other parents decide.

If nearly everyone vaccinates, herd immunity – essentially, vaccinating enough people – will stop the disease's spread. But once herd immunity is achieved, individual parents may decide that not vaccinating is the less risky option for their kid.

In other words, because of a fundamental tension between individual choice and collective welfare, relying solely on individual choice may not achieve public health goals.

This makes vaccine decisions fundamentally different from most other health decisions. When you decide whether to take medication for high blood pressure, your outcome depends only on your choice. But with vaccines, everyone is connected.

This interconnectedness has played out dramatically in Texas, where the largest U.S. measles outbreak in a decade originated. As vaccination rates dropped in certain communities, the disease – once declared eliminated in the U.S. – returned.

This isn't coincidence; it's game theory playing out in real time. When vaccination rates are high, not vaccinating seems rational for each individual family, but when enough families make this choice, collective protection collapses.

The free rider problem

This dynamic creates what economists call a free rider problem. When vaccination rates are high, an individual might benefit from herd immunity without accepting even the minimal vaccine risks.

Game theory predicts something surprising: Even with a hypothetically perfect vaccine – faultless efficacy, zero side effects – voluntary vaccination programs will never achieve 100% coverage. Once coverage is high enough, some rational individuals will always choose to be free riders, benefiting from the herd immunity provided by others.

And when rates drop – as they have, dramatically, over the past five years – disease models predict exactly what we're seeing: the return of outbreaks.

Game theory reveals another pattern: For highly contagious diseases, vaccination rates tend to decline rapidly following safety concerns, while recovery occurs much more slowly.

This, too, is a mathematical property of the system because decline and recovery have different incentive structures. When safety concerns arise, many parents get worried at the same time and stop vaccinating, causing vaccination rates to drop quickly.

But recovery is slower because it requires both rebuilding trust and overcoming the free rider problem – each parent waits for others to vaccinate first. Small changes in perception can cause large shifts in behavior.

Mathematics also predicts how people's decisions about vaccination can cluster. As parents observe others' choices, local norms develop – so the more parents skip the vaccine in a community, the more others are likely to follow suit.

Game theorists refer to the resulting pockets of low vaccine uptake as susceptibility clusters. These clusters allow diseases to persist even when overall vaccination rates appear adequate.

A 95% statewide or national average could mean uniform vaccine coverage, which would prevent outbreaks. Alternatively, it could mean some areas with near-100% coverage and others with dangerously low rates that enable local outbreaks.

Much more helpful would be approaches that acknowledge the tensions between individual and collective interests and that work with, rather than against, the mental calculations informing how people make decisions in interconnected systems.

In a 2021 study of a community with falling vaccination rates, approaches that acknowledged parents' genuine concerns while emphasizing the need for community protection made parents 24% more likely to consider vaccinating, while approaches that emphasized personal responsibility or implied selfishness actually decreased their willingness to consider it.

This confirms what game theory predicts: When people feel their decision-making is under moral attack, they often become more entrenched in their positions rather than more open to change.

Better communication strategies

That may sound obvious, but it's often missing from public discussion. Also, different communities need different approaches – high-vaccination areas need help staying on track, while low-vaccination areas need trust rebuilt.

When parents understand that vaccination protects vulnerable community members, like infants too young for vaccines or people with medical conditions, it helps bridge the gap between individual and collective interests.

Health care providers remain the most trusted source of vaccine information. When providers understand game theory dynamics, they can address parents' concerns more effectively, recognizing that for most people, hesitancy comes from weighing risks rather than opposing vaccines outright.

I wrote this before….

SCIENCE ISN'T MATH.

It never was.

And it sure isn't now.

The history of science is littered with "no wait....that's wrong...THIS is right..." going through the rinse and repeat cycle endlessly.

And that's ok. Inquiry and challenge and "being a science heretic" is, in many ways, how mankind learns more and can fix more problems.

One of my favorite sagas regarding "accuracy" and "settled science" is ulcers.

In 1981 Barry Marshall began working with Robin Warren, the Royal Perth Hospital pathologist who, two years earlier, discovered the gut could be overrun by hardy, corkscrew-shaped bacteria called Helicobacter pylori. Biopsying ulcer patients and culturing the organisms in the lab, Marshall traced not just ulcers but also stomach cancer to this gut infection. The cure, he realized, was readily available: antibiotics. But mainstream gastroenterologists were dismissive, holding on to the old idea that ulcers were caused by stress.

Unable to make his case in studies with lab mice (because H. pylori affects only primates) and prohibited from experimenting on people, Marshall... ran an experiment on ...himself. He took some H. pylori from the gut of an ailing patient, stirred it into a broth, and drank it....Back in the lab, he biopsied his own gut, culturing H. pylori and proving unequivocally that bacteria were the underlying cause of ulcers.

For their work on H. pylori, Marshall and Warren shared a 2005 Nobel Prize. Today the standard of care for an ulcer is treatment with an antibiotic.

But science isn't math. Your checking account balance is the sum of deposits less sum of withdrawals. Always. Forever.

The problem arises when people try to equate science with math...usually they call it "settled science." And, to be sure, robust inquiry and disciplined application of the scientific method usually gives you clear and distinct results. Then, science is settled...until we get new data or better techniques, and then we get "wait a minute..".

For example, there was a most excellent article posted on how "settled science" wasn't so settled, wherein:

seems that Earth has been misplaced. According to a new map of the Milky Way galaxy, the Solar System's position isn't where we thought it was. Not only is it closer to the galactic centre - and the supermassive hole therein, Sagittarius A* - it's orbiting at a faster clip.

It further noted other "errors" in SCIENCE:

A good recent example of this is the red giant star Betelgeuse, which turned out to be closer to Earth than previous measurements suggested. This means that it's neither as large nor as bright as we thought. Another is the object CK Vulpeculae, a star that exploded 350 years ago. It's actually much farther away, which means that the explosion was brighter and more energetic, and requires a new explanation, since previous analyses were performed under the assumption it was relatively low energy

The other problem arises when Certain Powers work overtime to suppress assiduous inquiry. Which, is what we have today as well. It's a bad double whammy.

In the interest of full disclosure, my "science isn't math" quote came from a recent post on social sciences, that featured this brilliant give and take involving a Harvard faculty member critical of Charles Murray from the original article, that is worth reprinting - it is with regard to the "certainty of SCIENCE":

"so why should we let someone teach social science that we know to be wrong in our social science courses?"

Because it is possible that you are wrong.
Science is not mathematics. Newtonian physics was wrong. And social science is a further three rungs down in certainty from science.

Your level of certainty and arrogance about what can be said, and probably thought, smacks of religion, and not science. This is a political religion that permeates academia at the moment. And which I am fairly sure you will swear does not infect you, while the rest of us can see the symptoms quite plainly.

Only religions ban heretics from speaking because of the wrong-think they might cause. Real science loves a good heretic. In fact, honestly, the entire goal of science is to be a heretic. To have an idea that no other person ever had. Science is the pretty much the antithesis of your thought-police approach.

And most of academia used to be the antithesis of your thought police approach as well, until the religion of leftism took it over, with the direct help of people like you.

They still don’t get it.

I’m sure there are some that count on others being vaxxed, but I think the more common risk being weighed is what disease is actually being treated vs the risk you’d acquire it otherwise.

E.g. Measles - a definite good vax choice. Common and if not vaxxed, very likely to get.

HPV - No. While it’s true that your daughter may become the whore of the town at 8 years old, most don’t. The caveat - if I’m the type of parent that encourages sexual proclivity, yes in the preteen years. If not, let them know of the option in latter teen years.

Flu - Again no, unless there is some other health problem risk factor. Too common and easy to acquire some herd immunity due to its prevalence. Plus, these vaxes are not actually updated as often as you think.

Last I checked in 2022, the flu vax was against strains prior to 2020. Though they do check what strain is prevalent every year, they usually consider the prior year’s vax sufficient. This makes it mostly useless - the odds are you were exposed to the strain since the last the vax was updated so why bother?

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