Doubt and Denialism: Vaccine Myths Persist in the Face of Science

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Bordetella pertussis, the bacteria that causes pertussis (whooping cough) magnified 40,000 times under an electron microscope. (The image is colorized.) Bacteria cling to the cilia of the respiratory epithelial cells, paralyze cilia with toxins, and cause inflammation and dense mucus in the airways that induce coughing fits. Before a pertussis vaccine become available in the 1940s, pertussis was one of the most common childhood diseases and a major cause of death among children. Those who survive infection become immune to the disease, though public health officials think natural immunity, like vaccine-induced immunity, wears off. (Image: Energeo EU)

As a science journalist, I’m often confronted with the unsettling fact that a sizable portion of my audience rejects what scientists know is true.

Take two classic cases, climate change and evolution. Even though two-thirds of Americans believe global warming is happening (up 3% from last year), less than half think we’re to blame. Just 15% of Americans believe humans evolved over millions of years from archaic species, while 46% think God created us pretty much as-is sometime within the past 10,000 years. That’s right, 46%—a figure that’s barely budged since Gallup started asking the question 30 years ago.

But it’s yet another evidence-impervious belief that I find most troubling. Last year, a Harris Interactive/HealthDay poll found that 18% of Americans think vaccines cause autism—a theory that has no basis in scientific reality, doesn’t even have a plausible biological basis, and has been knocked down more times than a metal duck in a shooting gallery. (Nearly a third aren’t sure if there’s any connection, while just over half think none exists.)

The blithe rejection of scientific knowledge in favor of, well, fantasy has become so common that it now has a name: “denialism.”

Denialism can take many forms, but most scholars agree that simply raising doubt about an issue can undercut the legitimacy of an entire corpus of scientific evidence in the public’s mind. And tactics for raising doubt abound. Those identified by infectious disease experts in a 2009 commentary include charges of conspiracy—for example, accusing vaccine advocates of profiting from the “vaccine-industrial complex”—and creating impossible expectations of what science can do—“absolute proof” that vaccines are safe, most recently raised by one-time “Saturday Night Live” cut-up Rob Schneider in a bizarre interview. I must point out that in peddling his vaccine-autism insanity, Schneider noted that autism was “nearly unheard of in the 1930s.” No joke. I guess he didn’t realize the syndrome wasn’t described until 1943.


Opportunistic Pathogens
In a way, that 18% still believe vaccines cause autism shows progress—down from 25% just two years ago. But unlike the idea that humans spontaneously appeared through an act of God, believing against all evidence that vaccines cause autism (or ill-defined harm) can have dangerous consequences.

Last month, CDC officials reported more than 18,000 cases of whooping cough (or pertussis) across the country—a rate of infection they hadn’t seen so early in the year since 1959. So far, nine babies have died.

California had its own epidemic in 2010, with more than 9,100 cases and 10 infant deaths.

Pertussis is a vaccine-preventable disease. But prevention depends on public compliance. And people like Schneider who doubt vaccine safety tend to consider their children’s vaccinations optional. In the 2011 poll, 86% of doubters opted out of some or all of their kids’ scheduled shots. That’s why some blame vaccine skeptics for the current epidemic. With just 84% of toddlers fully vaccinated, it’s likely skeptics play some role.

But CDC officials aren’t sure what’s behind the epidemic, or why even vaccinated teenagers are getting sick. It’s possible that the vaccine isn’t as effective as researchers hoped or has been targeting the wrong pathogen strains.

polio vaccine poster
The CDC’s national symbol of public health, the "Wellbee", appears in this 1963 poster to encourage the public to get the oral polio vaccine. (Image: CDC/ Mary Hilpertshauser)

What officials do know is that unvaccinated kids are eight times as likely to get pertussis as vaccinated kids. And when vaccinated kids do contract the disease, it’s much milder, doesn’t last as long, and tends to be less infectious.

That’s why public officials are urging adults, especially pregnant women, to get boosters to protect children still too young to be fully vaccinated. Kids get the first of five pertussis shots (plus a later booster) at 2 months. Most pertussis deaths claim children younger than 3 months old. Nine of the 10 children who died in California during the 2010 outbreak were under 8 weeks old.

Separating Fears from Facts
All this weighed heavily on my mind last week, when I wrote about new research that could conceivably feed vaccine doubts. The study, a fascinating investigation of experimental evolution in lab mice, found that vaccines can favor the evolution of more virulent malaria parasites.

Vicki Barclay (a postdoc in evolutionary biologist Andrew Read’s group at Penn State University) vaccinated mice with a malaria protein found in several vaccines now in clinical trials. She mimicked natural disease transmission by using needles instead of mosquitoes and letting parasites grow in one mouse before infecting the next one. (She did the same thing with unvaccinated mice.) Parasites that evolved in immunized mice caused more severe disease symptoms than those that evolved in unvaccinated mice.

Inevitably, some will misconstrue these results to confirm their belief that vaccines aren’t safe. Except the findings don’t say anything about vaccine safety. They show that, from a pathogen’s point of view, medical technologies act like any other selective pressure. We spend billions to develop the most powerful drugs science can muster only to discover we’re outnumbered, outgunned, and outmaneuvered. Millions of years of evolution have endowed pathogens with survival strategies we’ve yet to imagine.

Lest you delude yourself into thinking we humans have an edge in this evolutionary battle, consider this: Scientists have managed to wipe out just one human pathogen. Ever. After Edward Jenner discovered a smallpox vaccine in 1798, it took nearly 200 years and an all-out international effort to eradicate this disfiguring disease.

As Read and Barclay’s study shows, when you try to kill pathogens, they fight back. And when vaccines don’t destroy all the parasites (like the malaria vaccine now in clinical trials) or fail to provide lifelong immunity (like the pertussis vaccine), the survivors can evolve. And they might come back even stronger.

I know that most people who shun government vaccine schedules have their children’s best interests at heart. Some truly worry that vaccines may somehow cause irreversible damage to their child—and if it happened, how could they ever forgive themselves?

But anyone who chooses not to vaccinate their kids is missing something critical: the pathogens vaccine researchers are trying so desperately to control are formidable opponents. And though scientists still have a lot to learn about how pathogens adapt to our efforts to control them, they’re sure of this much: vaccines aren’t the enemy.

Vaccines rarely provide 100% protection. But they’re the state-of-the-art defense against infectious disease.

What’s more, if vaccine-preventable diseases like pertussis become more virulent, and there’s some evidence that this may be true, those who refuse vaccination will have little recourse when their kids—or their neighbors’ kids—take ill.


Public health officials often say that parents who reject vaccination will realize they’ve made a terrible mistake only when these once rare childhood diseases, long controlled by vaccination, return, with tragic consequences. Why on earth would anyone want to help a deadly agent hell-bent on survival get the upper hand?