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Vaccine safety and effectiveness are settled science

Lately, I have been reading nonsense from anti-vaxxers that laugh when I say “vaccine safety and effectiveness are settled science,” but it’s clear that they don’t understand the term, “settled science.”

For years, I’ve seen anti-vaxxers demanding a vaccine debate between well-known vaccine deniers, like Robert F Kennedy, Jr and Del Bigtree, and legitimate vaccine scientists and experts. The problem with these debates is that one side, pro-vaccine, uses the settled science, and the other side, anti-vaccine, employs all kinds of feints, logical fallacies, conspiracy theories, and false claims to try to “unsettle” the science

Settled science isn’t a term that is lightly given to a scientific topic. Human-caused climate change, evolution, gravity, and, yes, vaccine safety and effectiveness are settled science. It does not mean that we, as scientists, will ignore new evidence, it means that as it stands today, the evidence is overwhelming.

People will claim that all the noise and political debates about climate change, evolution, or vaccines means that there is a scientific debate. Hardly. Most scientists, and especially vaccine scientists, shrug their collective shoulders and wonder what is going on.

There aren’t any debates on any of these (and hundreds of other) scientific topics. Just because someone, like RFK Jr or Bigtree, thinks that there is some “debate,” it doesn’t mean there actually is one. All that happens is one side, almost always the science deniers, use misinformation, lies, anecdotes, and pseudoscience while attempting to scream and yell as loud as possible, then claim they’ve won.

Science can’t be debated. And there is no debate about vaccine safety and effectiveness because it’s settled science. Vaccines are safe and effective, and there is overwhelming evidence supporting the settled science

vaccine debate
Photo by Kyle Glenn on Unsplash

What is science?

Science is an evidence-based systematic analysis, without an inherent opinion or emotion, that answers questions about the natural world. In other words, it is a method to cut through opinions and anecdotal observations, so that one can have some reasonable expectation the proposed scientific principle can work as predicted.

This can be an issue when interpreting medical or scientific studies. Science tends to be written in nuanced, carefully supported statements. They often appear to be a bit indecisive, but it’s not.

Science is not dogmatic. Pseudoscience, religion, and alternative medicine are, by definition, dogmatic.

Moreover, science is binary – either there is evidence to support a hypothesis or there is not. Thus, if I propose the hypothesis that “vaccines are not linked to autism,” it is supported by a boatload of powerful evidence. On the other hand, the alternate hypothesis,” vaccines are linked to autism,” is not supported by any credible, peer-reviewed, high-quality published papers.  

But all vaccine scientists are open-minded to the potential that evidence could be presented that establishes a link between vaccines and autism. But it cannot be done through a “vaccine debate,” it only can happen with real evidence. If you think that the settled science of vaccine safety and effectiveness should be “unsettled,” then bring evidence that supports the unsettling. It’s easy (not really, but that’s why science is hard).

When a science denier states that “it has been proven,” (see Note 1) one must ask, “where is the evidence?”  What is more troubling is that someone who believes in this pseudoscience, such as vaccines causing autism, cannot imagine that they are wrong. Ironically, those of us who study real science almost always assume that the conclusions could be shown to be false with more evidence.

Whenever I hear that a scientist says, “we were wrong, it doesn’t work,” my response is “excellent, good science.” Pseudoscience never admits it’s wrong, so the pseudoscientist can claim “science isn’t perfect, so it can’t be trusted.”

Lucky for us, science works despite the various tropes of the pseudoscience world. 

two clear glass jars beside several flasks
Photo by Pixabay on

Scientific method and vaccine settled science

The other reason that a vaccine debate has no meaning is because of the underlying principle of science — the scientific method.

The scientific method is an unbiased systematic approach to answering questions about the natural world, including medicine. People tend to think “science” is some magical way to explain things run by magicians called “scientists.” But real science is a rational methodology to get at facts.

We didn’t conclude that evolution occurred by natural selection in a couple of hours – it took at least two centuries to get where we are. And now evolution is simply an observed fact, no different than light causes heat, and gravity pulls the apple down from the tree.

We also didn’t conclude that vaccines are safe and effective because Paul Offit said it was so. It’s because he utilized mountains of evidence to come to that conclusion. 

The scientific method has several basic steps:

  1. Define the question – this could be anything from “does this compound have an effect on this disease?” or “how does this disease progress?”
  2. Observations – this is the subjective part of science. Do we observe trends or anomalies? Does a physician notice that every patient from a town or neighborhood exhibits the same disease? A lot of science arises from observations of the natural world, and yes, some of those observations can be anecdotes or personal observations. For example, one of the most famous stories in the early history of medicine is when Edward Jenner observed that milkmaids rarely were infected by smallpox because they were exposed to cowpox, a less virulent disease.
  3. Hypothesis – using the observations, create a hypothesis that can be tested. In Jenner’s case, he hypothesized that exposure to cowpox immunized individuals to smallpox.
  4. Experiment – simply, the scientist then tests the hypothesis with experiments and collects the data. The experiments are not designed to solely validate the hypothesis but may also attempt to refute it. In real science, attempting to nullify one’s own hypothesis is an honorable pursuit.
  5. Analyze – examining the results carefully, usually using acceptable statistical methods to determine if the hypothesis was supported or not.
  6. Interpret – sometimes the data leads to a revision of the hypothesis, which means the scientist has to return to steps 3-6. Or it confirms or supports the hypothesis, which means the researcher can move to Step 7.
  7. Publish – in today’s scientific community, scientific data, and analysis are subject to the scrutiny of other scientists before they can be published, a process called “peer review.” This is a critical step that ensures that the results can stand up to criticism from other scientists.
  8. Retesting – many times the research is repeated by others, or the hypothesis may be slightly revised with additional data. Science is not static, it constantly revises theories as more data is gathered. For this reason alone, science is not absolute, it is constantly seeking new data.

This is not an easy process. It requires years of research by experts who spent years of study and research getting there. To think that one can do it in a few hours of Google research, which is definitely not the scientific method, is arrogance. And it is not the basis of an evolution debate, a vaccine debate, or a climate change debate. That’s for politics, not science.

vaccine debate

Vaccine settled science — no debate

Science is difficult, and that’s why there are people who spend tens of thousands of hours studying just one part of vaccines. As I’ve written before, a physician will spend around 11 years studying science and medicine before they are even close to being an expert on vaccines. A climate scientist may spend twice that long to be an expert on a small portion of the whole science of climate change.

Only arrogance and a strong dose of Dunning-Kruger cognitive bias empower the non-expert to think they have the ability to debate the overwhelming scientific consensus on so many different scientific issues.

Why do people give false balance to someone, without the expertise or education in the field, as if they know more about the issue than does the scientist? To many people, all we have to do is watch two people on a stage, and whoever appears to be credible or yells the loudest or looks the best, and then we can declare a winner, irrespective of what real science may say.

Let’s go with an example that has nothing to do with vaccines or climate change or evolution.

I think we can all agree that becoming a world-class architect is difficult. And then designing a new skyscraper isn’t easy, especially to keep it safe and beautiful. However, for those of us who are not architects, we tend to accept that the building isn’t going to topple over in a stiff wind.

Do we presume to know how the foundation has to be built to support the building? Or what materials are used to give flexibility in the wind, but strong enough to not collapse? Mostly, we don’t have a clue, but we trust that there isn’t a massive conspiracy to build unsafe skyscrapers because architects are being paid off by Big Concrete to use cheaper materials.

We generally don’t question the architects’ motives or whether they use solid engineering principles. 

We should treat science in the same way. We should accept scientific principles without doing the research ourselves – and once again, that’s not reading a few biased articles on the internet, assuming that we are now as smart as the researchers doing years of intense scientific study.

Of course, as I’ve written above, science is not dogmatic. If you want to dispute the settled science of any topic (vaccines, evolution, climate change, or whatever else), then you have to bring scientific evidence that meets the standards of the scientific evidence.

You do not get to whine about conspiracies, the validity of peer review, or anything else. Just bring evidence to refute the science, but it better be approximately equivalent to the quality and quantity of evidence supporting the consensus. An opinion piece in a predatory journal doesn’t count as science.

Part of the problem with these fake debates is that the public falls for the false equivalence logical fallacy. Presenters, whether it’s the news or giving us a pseudo-debate,  think that to be balanced, both sides of a scientific argument are equivalent in quality of opinion and evidence. Just watch a presentation on any of the major news outlets on any scientific topic.

They’ll have one talking head, a scientist who is trying to present nuanced data and who might be uncomfortable with a public “debate,” going up against a photogenic, possibly a scientist (but in a field totally unrelated to climate studies), who uses logical fallacies and manipulated data to make a point.

At this point, the viewer might think that half the world’s scientists are equally split between both sides of the “debate” regarding anthropogenic climate change (global heating). However, the real balance would give us 97 scientists supporting anthropogenic climate change and 2-3 against it. Yes, a high impact factor, an extremely well-respected journal, the Proceedings of the National Academy of Science, analyzed climate change science and determined that 97-98% of researchers in climate science supported the tenets of human-influenced climate change.

This is the same for the so-called vaccine debate – the overwhelming majority of physicians and scientists involved with vaccines (see Note 2) strongly support the settled science of the safety and effectiveness of vaccines. There is no vaccine debate, except in the minds of a tiny minority of people who reject science for their own ignorance.

Unless you like cherry-picking, confirmation bias, selection bias, Gish gallop, Argument from ignorance, and other logical fallacies, then a vaccine debate (or any science debate) is ridiculous. 

Research for anti-vaxxers. Photo by Rajeshwar Bachu on Unsplash.

False equivalence to refute vaccine settled science

Because I am an annoying old scientist, I’m going to repeat myself.

Evolution is an observed fact. The scientific theory of evolution describes the mechanisms that lead to the observed fact.

Anthropogenic climate change or global warming is an observed fact. The theory of climate change describes how humans have caused global heating.

Vaccines are, in fact, safe and effective (see articles, here, here, here, or here, if you need evidence with lots of peer-reviewed articles).

And in case you are wondering, the earth is 4.5 billion years old, the universe is 13.75 billion years old, HIV causes AIDS, and germ theory is real. 

And I could go on and on.

But the science deniers who want to create these fake debates try to use some ridiculous techniques to create a false equivalence. 

1. Claim science is a democracy

Science deniers love to make a case that every scientific principle is subject to some vote where a simple majority “elects” a new scientific theory or claim. They try to accumulate “voters,” generally scientists with little to no knowledge of the science, to make it appear that they have huge support for their ideas.

As I wrote above, science is built upon the scientific method, which is a logical process of observation, experiment, analysis, and publication. It is simple, but it requires work. Over time, after numerous experiments, nearly always published in peer-reviewed journals, followed by frequent repetition (and sometimes failure) of the experiments and results by other scientists, scientists arrive at a consensus about the evidence that supports a particular set of principles about the science being researched.

As the evidence accumulates and the science becomes more predictive, a scientific theory, which is a series of statements about the causal elements for observed phenomena, is formed out of the accumulated knowledge and predictability. These theories explain aspects of the natural world. They are predictive. And they can be tested through the scientific method.

Arriving at a scientific consensus is not something that happens overnight, but it is rather glacial in pace. The scientific consensus is NOT a result of a vote, it is based on the accumulation and preponderance of evidence that supports a claim. Like vaccines are safe and effective.

This process is a good thing. It keeps out poorly supported ideas but gives strength to ideas that have lots of supporting evidence. From those basic principles, science expands or improves over time.

One does not decide that the consensus is wrong through debate or argument — changing the consensus requires as much research based on the scientific method, as many peer-reviewed publications, and as much critique, repetition, and review as the evidence that built the original consensus. There isn’t a meeting somewhere where we vote for a new theory. It happens organically as evidence accumulates.

But if we did get together to vote, the votes for anthropogenic climate change, evolution, the safety and effectiveness of vaccines, and other fields would be overwhelming. In politics, that would be called a landslide.

2. Appeal to authority

Closely tied to the claim that science is some sort of democracy, denialists rely upon the argument from authority, a logical fallacy that provides an argument from an authority, but on a topic outside of the authority’s expertise or on a topic on which the authority is not disinterested.

So, when trying to create a false equivalence (and thus a public debate), denialists will bring individuals with credentials (whether valid or not) to the debate. But again, one authority person does not outweigh the vast numbers that are usually on the other side of the argument.

Vaccine denialists love to use Andrew Wakefield or Sherri Tenpenny, physicians who, in general, claim that vaccines are either ineffective, dangerous or both, as their authoritative source for vaccines. These individuals lack any real knowledge of scientific research and have never studied vaccines at the level of real biomedical researchers. But because they have “Dr.” before their name, the anti-vaccine pushers use them as their “proof” of vaccine problems.

3. Conspiracies

And tied to both the above, denialists love claiming that there is some conspiracy between all the world’s scientists to suppress or fabricate evidence. This incredible leap of irrationality would depend upon all the millions of scientists working together to invent data to show that evolution is true., that global heating is happening. that vaccines are safe and effective, or that the earth is 4.5 billion years old.

A few years ago, emails were hacked at the Climate Research Unit of the University of East Anglia in the UK. The emails were taken out of context and used by climate change deniers to “prove” there was a conspiracy. Of course, there wasn’t any conspiracy, but there were typical discussions of data by real scientists who were frank and honest.

And the data discussed was a small part of the total mountain of data supporting global warming — but in the world of false equivalence, this one set of emails, which proved nothing that was claimed by the climate-change deniers, was considered an important justification to show that there was a massive conspiracy to fake data about climate change.

Except for a few facts like – the emails didn’t say what the deniers think they say, and that even if there was a problem with the data, it was on one tiny little corner of the whole mountain of evidence supporting anthropogenic climate change. The science behind anthropogenic climate change is unchanged and powerful.

science deniers

4. Manufactroversy

Sometimes denialists will manufacture or invent a controversy, sometimes called a manufactroversy. Journalists frequently fall for this invention and attempt to create a false balance between both sides, right out of the thin air of the internet.

The vaccine deniers have done a good job trying to create an illusion that there is some sort of scientific debate ongoing with regard to vaccines causing autism. The thoroughly and scientifically debunked link between vaccines and autism continues to appear because some journalists make it appear that there are two equal sides to the debate.

With respect to this fake vaccine debate, one side, science, has literally dozens of clinical research studies that show there is no link between vaccines and autism. None.

On the other hand, anti-vaccine pseudoscience has nothing.

In other words, evidence matters. Quality of evidence matters. The quantity of quality evidence matters most of all.

There can be a political debate about vaccines

Political issues about vaccines can be debated. For example, vaccine mandates, especially in the world of the COVID-19 pandemic, have been a huge political debate. Now, that’s a political decision, somewhat outside the realm of science. But if the anti-mandate group tries to use bad science to support their claims, then it the debate overlaps with science.

However, a lot of pro-mandate claims are based on sound science and, frankly, Supreme Court precedence (at least in the USA). However, most anti-mandate people base their claims on political expediency and bad science like overstating vaccine side effects.

Thus, if RFK Jr or Del Bigtree wanted to debate mandates as a political issue, I have no problem with it. But if they reject mandates because vaccines cause autism (again, they don’t) or that the COVID-19 vaccine harms your DNA, then they’re trying to conflate a political decision with science. And they are almost always on the wrong side of vaccine science, so it’s hard to take them seriously if they want a great debate on vaccine mandates.

Clearly, any debate about mandates would wander to science, and then the anti-vaccine forces will claim that the science of vaccines is also subject to debate. And it isn’t.

Obligatory cute puppy photo. Photo by Daniel Milia on Unsplash

Summary of the vaccine settled science

These silly “science debates,” especially the vaccine debate are not debates. A debate requires two sides to have evidence supporting their claims. A vaccine debate has one side with evidence and facts, and the other with, well, nothing. 

Once a pro-science individual stands on the metaphorical stage to “debate” the other side, it makes it appear that there is a scientific debate, when there isn’t one. 

Carl Sagan once said that “extraordinary claims require extraordinary evidence.” Well, if someone wants to create an extraordinary dispute, it will also require extraordinary evidence that there is actually an extraordinary dispute going on. There isn’t one.

The settled science of vaccine safety and effectiveness is based on extraordinary evidence. It will require an equivalent level of extraordinary evidence to contradict the settled science of vaccine safety and effectiveness.

If some creationist, anti-vaccine zealot, climate change denier, or any other pseudoscience adherent wants to “debate” science, then they need to do the hard work. They must present scientific evidence, not anecdotes, lies, and misinformation, that has been published in respected biomedical journals. Then, if that evidence is powerful enough, then a scientific debate may ensue to determine if we should re-examine the consensus. This happens frequently (see Note 3), but again, only with that standard of “extraordinary evidence.”

This desire of the anti-vaccine squad to have a vaccine debate is a useless exercise that only set up real scientists to become a meme where the deniers will claim “we won.” The only way they can create a scientific debate is to provide peer-reviewed evidence that refutes the settled science of vaccine safety and effectiveness.


  1. Science rarely uses the term “proven”, because the scientific method is not a system to make a definitive answer to any question – scientists always leave open the possibility of an alternative hypothesis that can be tested. If the alternate hypothesis can be supported through experimentation, then it can replace the original one.
  2. Vaccine science includes the fields of epidemiology, public health, immunology, virology, microbiology, pharmacology, and a few other scientific disciplines.
  3. One of my favorite stories about upending scientific consensus is the story about Luis Walter Alvarez, a Nobel Prize-winning physicist. He and his son, Walter Alvarez, proposed the Alvarez Hypothesis, which claimed that a large bolide impact near the Yucatan peninsula caused a mass extinction event about 65 million years ago. Before they found the evidence, we weren’t quite sure what caused the demise of non-avian dinosaurs (and many other species of organisms) during what is known as the Cretaceous-Paleogene extinction event. When they first proposed the hypothesis, they were ridiculed by nearly every scientist. However, the Alvarez team kept presenting powerful evidence that supported their claims. Today, the evidence is so overwhelming that most scientists consider it settled science. 

Key citations

  • Anderegg WR, Prall JW, Harold J, Schneider SH. Expert credibility in climate change. Proc Natl Acad Sci U S A. 2010 Jul 6;107(27):12107-9. doi: 10.1073/pnas.1003187107. Epub 2010 Jun 21. PubMed PMID: 20566872; PubMed Central PMCID: PMC2901439. Impact factor: 9.737.
  • National Institute of Allergy and Infectious Disease (2010). The Evidence That HIV Causes AIDS.
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