These outbreaks have caused the public health sleuths to search for the actual causes of this polio-like syndrome. And there just isn’t any robust or valid evidence that the polio vaccine is anyway related to acute flaccid myelitis.
As we know, polio can be a crippling and potentially deadly infectious disease caused by the poliovirus, a human enterovirus, that spreads from person to person invading the brain and spinal cord and causing paralysis. Because polio has no cure, the polio vaccine is the best way to protect ourselves from the crippling disease.
Because real scientists wanted to know what caused this acute flaccid myelitis outbreak, they tried to hunt down the actual cause. A recent study of most of the individuals who have contracted the disease seems to be narrowing down on a couple of culprits.
I originally wrote this article in 2014 to discuss whether correlation implies causation. Not that I expect everyone to read and remember this one article, but it’s frustrating when I see a conversation where people who deny science and accept science both misuse correlation and how it relates to causation. So, I decided to update this article and republish it as a reminder that the relationship of correlation to causation isn’t as easy as a simple trope or meme.
One of the foundations of biomedical science is whether correlation implies causation. Anti-vaccine activists often conflate or misunderstand the two, rejecting or accepting correlation as it fits its narrative. The “correlation implies causation” story is often abused, misused and confused by many writers.
One thing we do know about correlation is that if you can’t establish correlation, despite numerous attempts, it is nearly impossible to claim causation. Also, if you do observe correlation, it also doesn’t imply causation.
But there are methods, grounded in powerful science, to establish causation from observations of correlation. So sometimes correlation does not imply causation. But sometimes correlation implies causation.
How many times have you heard tiresome tropes about the HPV vaccine causing this or that? No matter how many times we debunk the nonsense, it persists. One of the critical points I try to make is that before an anti-vaccine claim can be made, there has to be a biological plausibility. That is, can we establish a reasonable and plausible biological mechanism, without resorting to special pleading and pseudoscience, that can lead one from one action, say receiving a vaccine, to some result, real or imagined.
Biological plausibility is a requirement to establish that correlation means causation. It is almost an essential requirement for one to claim a causal association. But biological plausibility must be consistent with our existing knowledge of biology, chemistry, physics, and medicine. How many times has an anti-vaccine zealot tried to convince us that “mercury in vaccines causes autism” but ignores the basic scientific tenets of numerous fields of biomedicine like biochemistry, cell biology, toxicology, immunology, neurology – well, just about every field?
Or someone who claims that acupuncture treats a bunch of diseases, yet we cannot find any reasonable biological plausibility between sticking a needle in the arm to treating some medical condition like pain. They tend to ignore that by using their own personal anecdote as “proof.”
That’s why science is much harder than what is said by the pseudoscience pushers. Establishing plausibility requires a strong knowledge of science to make the case. It’s much more than simply stating that plausibility does exist, you have to use actual real science, published in real scientific journals, to make the case.