It's not just the myth about autism that's driving down vaccination rates. Many parents believe that as long as most other children are vaccinated, their kids won't get sick. It's a faulty interpretation of "herd immunity" — and it's prompting families to prioritize exaggerated, imagined risks over actual benefits.

September is fast approaching, which means kids are getting ready to go back to school — and the headlines in newspapers across the country are telling a dismal story. "8,000 Children in Iowa Starting School Without Vaccinations," "Whooping Cough Cases on the Rise in Idaho: Officials Say Anti-Vaccination Beliefs a Factor," "More Maine Families Skipping or Delaying Vaccinations."

In Iowa alone, the number of parents who received vaccine exemptions is more than triple the number from 12 years ago. As the Des Moines Register reports:


Rick Kozin, Polk County's public-health director, said some parents apparently believe their children can skip vaccinations because most of their kids' classmates have received the shots. The parents figure there would be little chance of encountering the viruses or bacteria that the vaccinations target, he said.

Kozin said such parents might not realize that many other families are making the same calculation, which could open up a school to a disease outbreak. "I don't think some of these parents see the risk they're taking with their kids' health," he said.

The statistics blog, FiveThirtyEight, echoes that view:

There are many reasons people choose not to vaccinate their children…. Some object for religious reasons. In other cases, medical conditions make vaccination impossible or dangerous.

And there are still others who aren't necessarily convinced that vaccines are dangerous, but simply view the benefits as minimal. Why subject your child to a painful shot, given that you've never actually seen anyone get the measles? This logic relies on the idea that "herd immunity" will protect even unvaccinated children. If enough people are vaccinated against measles, then no one will get it, so even unvaccinated children will be protected.

In other words, parents are undermining the benefits of herd immunity by increasing the pool of susceptible children. Some of these parents are lulled into the belief that their kids will be safe because they read about the high vaccination rates in their respective states. For instance, in California, that rate is at 95%. And, in Iowa, just over 93% of toddlers receive shots for mumps, rubella and measles, which is around 2% higher than the national average.


But those numbers don't tell the whole story.

Local Conditions

FiveThirtyEight, for instance, takes a look at whooping cough and vaccinations by state. The relationship is negative: the higher the vaccination rate, the fewer the number of whooping cough cases:

Based on what we know about herd immunity, there is a sense in which the relationship for whooping cough is surprising. Estimates suggest a vaccination rate of 92% to 94% is high enough to confer herd immunity in whooping cough, and so a 95% vaccination rate should be high enough to deliver good protection.

The obvious explanation is that a 95% vaccination rate at the state-level doesn't mean that 95% of people are vaccinated everywhere in that state. When looking at county statistics, it's very clear that low vaccination rates increase disease outbreaks.

As FiveThirtyEight explains:

And it's notably the vaccination rates on the lower end of California's spectrum that really matter…..For whooping cough, disease rates are more than three times as high in counties with a vaccination rate lower than 86 percent compared to those with a rate above 94 percent.

For parents, this information would seem to caution against reliance on herd immunity. Yes, if your county (or better, your neighborhood) has a 99 percent vaccination rate, you're probably safe. But knowing that your state vaccination rate is 95 percent really isn't enough. For the vast majority of people, there is absolutely no medical reason not to vaccinate, and the idea that there are no benefits is foolish.

The Undervaccinated

As the public health site Disease Daily likewise observes:

The fact is that nationally, vaccination coverage is relatively high — but not high enough. We need exceptionally high immunization coverage against exceptionally infectious diseases, like measles. And worst of all, national averages can hide some local variances that create dangerous powder kegs for infectious disease outbreaks.

For example, in California in the 2007-2008 school year, 92.1% of kindergarteners were fully immunized — not bad, right? Well, unfortunately it's not that simple. Someplace like Glenn County reported 98.5% immunization rates — you go, Glenn Co! But… on the other hand, Nevada County reported that just 75.5% of its kindergarteners were fully immunized. That's not high enough to ensure herd immunity against many diseases, like measles or whooping cough. One infectious traveler entering that under-protected community could be the spark to start an outbreak.

But the problem is not simply parents who refuse to let their children get any vaccinations. Another issue is undervaccinated kids who have received one, some or even most of their vaccines, but are still missing some important ones. According to one research study:

Over 35 percent of children were undervaccinated to some degree. These children were statistically more likely to be racial or ethnic minorities, have a mother with low educational attainment, and live in poverty. These likely aren't kids whose parents are refusing to let them get vaccinated, but they might be having trouble seeing a provider regularly or paying for vaccines. They're falling through the cracks of the health system. This group is arguably the most important group for public health officials to focus on for outreach and more services.

It was such concerns that prompted the creation of the Vaccines for Children (VFC) program 20 years ago. Following an outbreak of measles that was responsible for 55,000 cases between 1989-1991, health officials reported that the resurgence of the disease was caused largely by the widespread failure to vaccinate uninsured children. The program was hugely successful, saving the lives of more than 732,000 children and more than $1 trillion in direct and societal costs. The racial/ethnic disparities in vaccine coverage shrank considerably, though it is clear there is still much to be done to decrease the number of undervaccinated children.

But then, there's the other group: the parents who willingly endanger their children and communities by undervaccinating their kids. Again, driven in part by the belief that most other children have gotten their shots, there are parents who would rather string immunizations out instead of getting them all at once — even though studies show immunizations to be more effective when taken in combination.

The Real Cause of Agony

Pediatricians report that one reason parents prefer to spread out or delay vaccinations is that they don't want to subject their young children to the pain of getting all of their shots at once.

Greg Laden, writing about the experiences of taking his own child to the doctor, says:

I'm pretty sure some anti-vaxxers … not the activists but just some of the parents who quietly chose to not have their children stuck … do so because they can't stand the needle, the pain, and (in some cases) the subsequent though generally very minor suffering or discomfort of a needle-wound or side effects of the vaccination. And I can understand that. When you see the infant you love being so brave in the face of the atrocities of the doctor's office, turning red, trying not to cry, lip quivering, finally breaking down, and that look … that look of betrayal … Yeah, I can see not wanting to do this too often.

But I do get Huxley vaccinated because 1) I'm not some kind of selfish moron who wants to avoid personal discomfort or self-blame for an infant's short-lived pain and b) I've seen the babies die, quietly at the end though often after days or weeks of very obvious pain and suffering, of infectious diseases. So when I watched Huxley take his shots like the man-infant he is, I simply reminded myself that this was better than an untimely burial.

Among the anti-vaxxers, this concern has recently taken an even more dangerous turn. As Chris Mooney reports in Mother Jones, parents are refusing to a allow their newborn infants to receive a standard vitamin K shot — which puts babies at risk of a condition called "vitamin K deficiency bleeding" (VKDB). "This rare disorder occurs because human infants do not have enough vitamin K, a blood coagulant, in their systems," Mooney writes. "Infants who develop VKDB can bleed in various parts of their bodies, including bleeding into the brain. This can cause brain damage or even death."

Along with all the usual pseudo-scientific rubbish that dissuades parents from giving infants this vitamin, there are the views expressed by one anti-vaxxer physician who says that shots cause pain that can result in permanent trauma:

Mercola suggests there is a "Potential Dark Side" to the vitamin K shot. "A needle stick can be a terrible assault to a baby's suddenly overloaded sensory system, which is trying to adjust to the outside world," it reads. (Although Mercola himself rejects and debunks the alleged leukemia link.) Mercola instead suggests administering vitamin K orally, claiming it's "safe and equally effective." [It isn't].

There might be one positive thing to come out of this tragedy of willful ignorance. A recent study reports that one way to predict which parents will reject vaccination for their children is to keep track of who refuses their baby a vitamin K shot at birth. Children whose parents declined vitamin K were 14.6 times less likely to be immunized with any recommended childhood vaccines by age 15 months, compared to kids who got vitamin K.

We might have an early-warning system that helps identify "vaccine-hesitant" parents — including those who are willing to take risks with children's lives under the misguided belief that, as long as other kids are vaccinated, everything will be just fine.