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My Hoover Institution colleague Kori Schake wrote about last Wednesday’s GOP debate that, when it comes to foreign policy, the contenders still have a lot to learn. The same is true about vaccines and vaccination policy.

Donald Trump claimed that pediatric vaccines have caused an alarming increase in autism, and that the pediatric vaccination schedule should be attenuated — that is, spread out with smaller doses over a longer time period. Trump is wrong on both counts, which is not surprising for someone who has no expertise in this area and tends to shoot from the hip on all manner of subjects; but the unwillingness (or inability) of the two physicians among the candidates — ophthalmologist Rand Paul and pediatric neurosurgeon Ben Carson — to set the record straight was appalling.

This contretemps follows similar recent missteps about vaccination by Carly Fiorina, Chris Christie, and Rand Paul (again), all of whom have suggested that parents should have the right to withhold vaccines from their kids. That makes sense only if you think parents should be permitted to let toddlers play with double-edged razor blades and cigarette lighters.

The most important facts relevant to the debate’s misapprehensions are these:

• There is no evidence that vaccination is in any way related to autism, more accurately called “autism spectrum disorder,” or ASD. Although it has been known that ASD runs in families, the underlying genetic determinants have been elusive, but a 2010 study published in the journal Nature offers some new insights. Drawing on data from 60 research institutions in twelve countries, the researchers analyzed the genes of 996 children with ASD and 1,287 children without the condition. They found that each affected person carried his or her own individual assortment of mutations. This contrasts with the situation in sickle-cell anemia, for example, where the disease is caused by a unique mutation — a change in one specific nucleotide of DNA, which in turn causes a single amino-acid change in a gene that codes for the protein of hemoglobin. (Genes are made up of DNA, which is a template that, after an intermediate step, directs the ordering of building blocks — amino acids — into proteins.)

Where and when do these ASD mutations arise? Professor Daniel Geschwind, chief of human genetics and director of the Center for Autism Research and Treatment at the UCLA School of Medicine, said the findings suggest that the tiny genetic errors may occur during formation of the parents’ eggs and sperm, and that these mutations are conveyed into the DNA of the offspring. The autistic offspring will be the first in his or her family to carry that variant. The parents don’t have it.

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• We have not been exposing children to more and more vaccine antigens (the substances in vaccines that actually induce the immune response) over the years. Quite the opposite, in fact: As of 2000, children received only about 4 percent as many antigens during the standard vaccination schedule as they did in the middle of the last century. In 1960, a child was exposed to approximately 3,200 vaccine antigens during the routine vaccinations; by 2000, that number had shrunk to around 126. Vaccines are continually becoming purer and more refined, which translates to greater safety and efficacy. The currently used pediatric and adult vaccines are superb, boasting some of the most favorable benefit–risk ratios among all pharmaceuticals we’re exposed to during our lifetimes.

• Spreading out vaccinations over longer periods than recommended exposes children to unnecessary risks because it leaves them unprotected for more time than is necessary — or safe. The vaccine schedules have been meticulously crafted to maximize both safety and efficacy, and they are the same ones followed in most industrialized countries.

#share#One mystery is why politicians don’t learn from their predecessors’ mistakes. In 2011, on CNN, Michele Bachmann said about the Human Papilloma Virus (HPV) vaccine, “The problem is, again, a little girl doesn’t get a do-over: Once they have that vaccination in their body, once it causes its damage, that little girl doesn’t have a chance to go back.” And the next day, on NBC’s Today program, she dug the hole deeper, charging that the HPV vaccine “can have very dangerous side effects,” including mental retardation, and that the vaccine “could potentially be a very dangerous drug.”

Bachmann was excoriated by the medical community for those remarks. The HPV vaccines are excellent. They prevent infection with the most common strains of human papilloma virus, which, once established, can cause genital warts as well as cervical, anal, vulvar, and vaginal cancers. Thus, by preventing the infection, the vaccine prevents all those sequelae. In the extensive clinical studies (on more than 20,000 girls and women) that were performed prior to the FDA’s licensing of the first vaccine, it was 100 percent effective, a virtually unprecedented result. How safe are the vaccines? No serious side effects were detected; the most common side effect was soreness, redness, and swelling in the arm at the site of the injection.

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Having spent 15 years as an official at the Food and Drug Administration and seen regulation — the good, the bad, and the ugly — up close, I am as opposed as anyone (except perhaps Rand Paul) to government intrusion into our lives. But some interventions are good, benefiting individuals and society as a whole; and compulsory vaccination to prevent childhood diseases definitely falls into that category.

For the past 50 years, parents of small children have not known the fear — much less the reality — of deadly childhood diseases, which used to claim the lives of one in six pre-schoolers. Until the mid-20th century, epidemics of highly communicable diseases such as diphtheria, measles, and whooping cough regularly killed large numbers of children and left others with permanent disabilities. When I was a child, my parents would not let me go to public swimming pools during the summer because of the threat of polio.

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But thanks to the miracle of vaccines, which are arguably the greatest public-health triumph of the 20th century, these devastating epidemics became rare and well contained. According to the Centers for Disease Control and Prevention (CDC), vaccines administered to American children between 1994 and 2013 will save 732,000 lives and prevent 21 million hospitalizations. (Think for a moment about the implications of those numbers — the misery and heartbreak avoided by vaccination.)

Now, however, infectious diseases are making an alarming comeback in this country. The culprits are parents who should know better — and politicians who accommodate them. A kind of amnesia about the threat of infectious diseases, combined with a fraudulent scare that supposedly linked autism to vaccines and skepticism about “synthetic chemicals,” has led to diminished compliance with vaccination schedules, which in turn has led to dangerous disease outbreaks.

More than 28,000 cases of pertussis (whooping cough) were reported to the CDC in 2014, an 18 percent increase over the previous year. Measles, the complications of which can include pneumonia, encephalitis, and death, is another viral illness that was almost extinct and now is experiencing a resurgence. Between 2001 and 2008, a median of 56 measles cases in the United States were reported each year to the CDC, but since then the incidence has been trending upward; in 2014 there was a spike, with more than 600 cases reported.

Such infections not only cause unnecessary morbidity and mortality, but exact significant health-care costs. A 2008 measles outbreak in Arizona that infected only 14 patients cost the two hospitals involved $800,000 to respond to the cases and contain the spread of the disease.

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In most states, children who do not have documented proof of up-to-date vaccinations are barred from school, but there are exceptions to the requirement. All 50 states exempt children if a doctor attests to a relevant medical condition, such as a vaccine allergy (quite rare). Most states permit exemptions on the basis of deeply held religious belief (with clerical documentation), and 20 states also allow so-called “philosophical” exemptions (also known as “personal belief exemptions,” or PBEs); the latter constitute the vast majority of exemptions. (California recently changed its law to get rid of the religious and philosophical exemptions; the new law will take effect in July of next year.) Some states are seeing exemption rates as high as 4 to 6 percent in kindergartners, and in some communities heavily populated by the New Age, Back to Nature, organic-everything crowd, the rates are alarmingly high.

Although competent adults should be permitted to make decisions about their own medical care — however unwise some of those decisions may be — withholding vaccines from children except for valid medical reasons is tantamount to withholding a needed blood transfusion or operation. It constitutes abuse. (And please spare me the Huckabee-esque prattling about religious freedom superseding anything and everything else.)

Putting an individual child at risk also puts the community at risk. Some of the recent outbreaks occurred when unimmunized or underimmunized travelers returned home from abroad, became ill, and infected other unprotected people. The higher the rate of vaccination in a community, the less likely it is for an epidemic to gain a foothold and spread. An important determinant of spread is whether there is “herd immunity,” an immunological barrier that blocks the spread of an infectious disease.

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Herd immunity appears when a large proportion (ranging from about 75 percent to 94 percent, depending on the infectious agent) of a susceptible population is vaccinated. The spread of the pathogen via person-to-person transmission is blocked when it confronts immunized, resistant individuals. But when community-level protection falls below a certain level, the infection rate rises precipitously. Thus, a high rate of immunization serves to protect everyone in the community, including those few who legitimately cannot be vaccinated or who mount a sub-optimal immune response, such as the elderly.

It is discouraging to encounter politicians who not only don’t know much about science, technology, or medicine (which is perhaps understandable) but also don’t know what they don’t know. Here’s my advice to the presidential hopefuls (which also applies to incumbents): If you’re not sure of the facts surrounding an esoteric subject like vaccination, read a good review article and consult an expert.

— Henry I. Miller, a physician and molecular biologist, is the Robert Wesson Fellow in Scientific Philosophy and Public Policy at Stanford University’s Hoover Institution. He was the founding director of the FDA’s Office of Biotechnology.