"We knew there was controversy when we got pregnant," Paul, who asked for his name not to be used because of concerns about public backlash, said over the phone from his San Francisco home. "It soon became clear that the most cited voices in the debate, like Jenny McCarthy, were non-medical."

Paul and his wife are both talented professionals; between them, they hold a total of six degrees. He works in software development, and she in medicine. They dug into the research on vaccine scheduling voraciously, wanting to understand what would be best for their infant son.

That's how they stumbled across The Vaccine Book by Bob Sears, a doctor from Southern California, who suggests parents can space out their vaccinations much more than the federal government recommends — or even skip some all together.

"Vaccination isn't an all-or-nothing decision," Sears writes, in his number-one bestselling children's health book. Some vaccine-preventable diseases aren't all that bad, he argues, and it's not clear why people still inoculate their kids for scourges like polio, a crippling disease that's no longer common in the US. So Sears — also known as "Dr. Bob" — suggests spreading out the shots, which allegedly cuts "the risk of having a severe reaction and avoids overloading babies with too many chemical ingredients."

"When you make this decision, it's something you have as a private bond. You never tell anybody."

Or, as he put it in the book: "It's the best of both worlds of disease prevention and safe vaccination."

Paul found the arguments convincing, comforting. "Dr. Sears wanted parents to be informed of the risks and benefits of all vaccines," he told Vox. While he absolutely believes in the importance of inoculation, he and his wife decided to delay their son's measles, mumps, and rubella shot. Instead of having him immunized at a year, they planned to wait until his third birthday.

He felt confident in his decision, but he also felt squeamish about how others would react, possibly grouping him in with Jenny McCarthy acolytes who disavow lifesaving inoculations altogether. "When you make this decision," he said, "it's something you have as a private bond. You never tell anybody."

A dangerous 2 percent

If you read the news today, you might think the country is facing an army of vaccine-refusing zombies who hate science and put the rest of us at risk for preventable diseases by shielding their own precious children from autism-inducing shots.

In reality, in America, the overwhelming majority of parents side with science: they choose to vaccinate their children. Vaccine requirements are set at the state level, and all 50 require parents to immunize their kids. Nineteen states allow medical, religious, and philosophical exemptions. Twenty-nine states and the District of Columbia allow medical and religious exemptions. West Virginia and Mississippi have medical exemptions only. All told, just 2 percent of the population rejects vaccines for their personal beliefs.

More common than outright vaccine deniers might be parents like Paul, who would be better described as delayers. They generally agree that vaccination is a public-health benefit, and they hate "anti-vaxxers." They're just hesitant and skeptical about some areas of vaccine science. As we've gone from one dose to more than 20 over the last 100 years, some parents have grown wary about inoculating their kids.

So they pick and choose among the vaccines they give their children. They delay some, and skip others. They think their self-styled schedules are safer than the one approved by the government. A majority of doctors submit to their whims. And they want public-health officials to acknowledge their worries about the potential risks of vaccines, however small they may be. Their concerns have arisen at a time when many of the scourges that formerly attacked Americans have largely disappeared from view. Among this group, vaccines are a casualty of their own success.

The the research we have on the delayers suggests they far outnumber the deniers. A 2011 survey of parents of young kids found that more than one in 10 reported using an alternative vaccine schedule; of those, 82 percent delayed one or more vaccine doses, believing that theirs was a safer approach.

One in ten American parents now use an alternative vaccination schedule

Researchers completely disagree with this vaccine-hesitant group: they say they are a public health threat, almost as bad as those who refuse inoculations altogether, because they put off vaccines that are timed according to the best-available science to keep babies healthy. They think their worries also undermine the decades of research that almost unequivocally shows vaccines are safe, and that they imperil society's "herd immunity" — the fact that even those who can't or don't get vaccinated are protected because diseases can't spread very far when most people are immunized.



So these people quietly benefit from parents who vaccinate their kids on time, which may be part of the reason the delayers hide in plain sight.

The totality of the research we have on vaccines is stacked against the delayers, said Dr. Doug Opel, a Seattle pediatrician who studies vaccines. "There is just no science to this. We immunize with this vaccine at this time because kids are most at risk at this point. They are most susceptible. What gets lost a lot of the time is that there's an incredible amount of data underlying the recommended schedule."

An "alternative vaccine schedule"



Underlying many of the concerns of vaccine skeptics today is a single fact: these needles and drops are preventive interventions, not curative ones, and so they may present a risk now in order to prevent a danger that may never happen later.

Doctors have to ask new parents to inject their perfectly healthy babies with viruses and bacteria to stop a potential future illness from ever happening. Over the last century, the number of recommended doses of vaccines kids get by the age of two has increased from one to more than 20.

Today's parents have never seen or experienced many of the illnesses they are fending off with all these shots. It may feel like a leap of faith to comply with these demanding immunization schedules, Eula Biss explains in her book, On Immunity: if you consider the history of medicine, for a long time, doctors did more harm than good. Bloodletting might seem insane now, but it was a routine practice for thousands of years. It's not entirely irrational that some parents might have some hesitancy about the profession, and volunteering their kids for this preventive medication.

In 2007, Bob Sears seized on that hesitancy. He presented what has become one of the most popular conventional vaccine alternatives of them all. The Vaccine Book is a turquoise manual, and most of its 19 chapters are dedicated to the author's take on a particular vaccine, from chickenpox to hepatitis A and the MMR. The book is popular, too, selling more than 180,000 copies as of 2012.

From a business standpoint, Sears is a genius: he capitalized on a moment when a (now thoroughly discredited) publication in The Lancet linked the MMR vaccine to autism, worrying even the most educated and science-minded parents.

The terror helped to drive down the rates of MMR vaccination in Britain, Ireland, the United States, and other countries, and fuel outbreaks of measles. Amid the anxiety, Sears offered a middle path: parents could vaccinate, just on their own terms. "Dr. Bob's Alternative Schedule" suggests potentially spacing out routine shots over 21 visits, as opposed to the standard 13 suggested by the CDC. He also sketched out another plan that involves selective vaccination.

From a scientific standpoint, Sears is a quack: while he claims to be a vaccines expert, he is not a researcher and has never conducted his own vaccine science. The book is filled with untested claims — albeit comforting and appealing ones — that fit in the realm of "belief," not "science." For his theories about "overloading" babies with vaccine chemicals and the potential dangers of the MMR, he has become the "bane of pediatricians' existence" — and with good reason.

"Too many, too soon"

One of the key concerns that alternative vaccine schedules try to address is that kids get too many shots too early, and their immune systems aren't ready for them. Sears pushes the idea that babies have underdeveloped immune systems, and exposing them to too many viruses or bacteria in too short a time might overwhelm their defenses.

So with Dr. Bob, kids can get the Hepatitis B vaccine at the age of two and a half, instead of one month, and the measles shot at age three instead of 12 months. Parents can skip some vaccines altogether, such as the one for chickenpox.

Another San Francisco vaccine-delaying parent, who also didn't want to be named, followed Sears' alternative schedule. Marie, a PhD in biomedical science, told Vox that her son had underlying health issues, and she was concerned vaccines might exacerbate them. When she posted on Facebook about her decision, her friends lashed back. They wrote things like, "You're a scientist, you should know better." "You should trust in science." "You understand the immune system." "I don't get why you're questioning this."

But Marie was worried about her son's epilepsy and how he might respond to vaccines. "I didn't want to overload my son's immune system and deal with a big nasty seizure and have a lot of other implications." Even though her second son had no other health issues, she followed Sears' schedule again, perhaps out of habit. "We delayed because we had done it with the first one," she explained.

Sears' theories may make a kind of intuitive sense, even to scientists like Marie. But according to the data mustered by the scientific community, he's simply wrong.

As researchers writing in the Oxford Journal of Clinical Infectious Diseases explained, "Although the infant immune system is relatively naive, it is immediately capable of generating a vast array of protective responses; even conservative estimates predict the capacity to respond to thousands of vaccines simultaneously."

A more recent study looked at the association between the number of vaccines kids get in the first two years of life and neuropsychological outcomes later in childhood. There was no association between the two.

The idea of suddenly "overloading" kids with shots doesn't actually make much sense based on what we know about the immune system, either. When babies are in their mothers' wombs, they are in a sterile environment. But as soon as they come down the birth canal, their bodies are very quickly assaulted with bacteria, both good and bad. Almost immediately, they need to fight off an average of four to six viruses per year.

Researchers argue that the weakened viruses in vaccines are literal drops in the ocean compared to the live ones kids encounter every day, explained Paul Offit, an infectious diseases doctor in Philadelphia. "The idea you're living in a more sterile world because you refuse to get these three very weakened vaccines is absurd," he said.

Rahul Parikh, a physician writing in Salon, put the "too many, too soon" argument in stark perspective. "While the notion of injecting a metal like aluminum into a baby isn't appealing to anybody," he wrote, "it has gone on for almost six decades." He explained that by six months, breastfed babies take in about 6,700 micrograms of aluminum. "Formula fed babies take almost 40,000 micrograms (116,600 micrograms if they drink soy formula). In that same period of time, the cumulative dose of aluminum from vaccines on the schedule I use to immunize kids in my office is a mere 4,575 micrograms."

"Polio is eradicated here. But we get all these polio vaccines."

When you talk to and read about vaccine-delaying parents, you come across a refrain: that many of the required vaccinations relate to diseases that don't affect people like us.

"Polio is eradicated here. But yet we get all these polio vaccines," the vaccine-delaying PhD, Marie, said. "We waited on the hepatitis B vaccine because we're not IV drug users, we don't live in a place where kids are going to have contact with IV drug users or prostitutes. And the other vaccines, we spread out."

But what's somehow lost on these intelligent people is that their arguments are entirely circular: the reason these diseases don't affect most Americans now is precisely because people like them have been using vaccines.

If we stop vaccinating, or put off giving them to kids in a way that exposes them to infection, these diseases will undoubtedly return.

For example, on the Hepatitis B vaccine, one of the reasons why the CDC switched from targeted immunizations to a universal vaccine was because of epidemiological science that showed the virus was being transmitted in settings like daycare, Seattle's Dr. Opel explained.

"A lot us think our kids aren't going to be exposed," he added, "they are not at risk for getting X, Y, or Z, but often these risks happen and our kids are exposed based on things we can't control."

The parents who took their kids to Disneyland in December probably didn't imagine they'd leave with an ancient virus, the measles. Many travelers to Europe, one CDC official told me, forget to check in on their vaccines because they don't think about the fact that diseases like measles are now prevalent in some parts of Europe.

That's what happened to one of Sears' very own patients: the child contracted measles on a trip to Switzerland. When the boy returned to the US, he infected 11 others. All it takes is a single traveler to hit a community of similarly unvaccinated people for an outbreak to spark.

What's worse, Sears has admitted there are dangers to too many people opting out, which is why he tells delayers to keep their decision secret. "I also warn them not to share their fears with their neighbors," he writes, "because if too many people avoid the MMR, we'll likely see the diseases increase significantly."

The MMR dangers?



Another notion delayers buy into is that the combined MMR vaccine is somehow more dangerous than others. On the face of it, this fear seems reasonable. Not only has the vaccine received an undue amount of bad press because of the debunked autism link, but as San Francisco vaccine delayer Paul explained, no other vaccine contains three live and weakened viruses.

"First, what's unique about is that you're injecting three live [weakened] viruses into a 12 month old. Their immune system won't encounter those naturally," he said. "Second, MMR produces more severe reactions than any other vaccine. It's not unreasonable to think that this might be due to the first point."

When asked whether this vaccine has led to more adverse events compared to other vaccines, Dr. Tom Shimabukuro, the deputy director of the CDC's immunization safety office, said "no."

The side effects, he explained, are rare and mostly very mild. According to CDC data, for example, fevers after the MMR vaccine occur in one out of six people, and mild rashes in one in 20. More severe problems are virtually non-existent: serious allergic reactions happen in less than one in a million cases. Deafness, long-term seizures, and permanent brain damage are "so rare that it is hard to tell whether they are caused by the vaccine."

Occasionally, young children have short-term seizures that are linked to fevers from the vaccine. But although they are surely frightening for parents, independent research has found they have no lasting effects.

As for death, again, this is an exceedingly rare event and most often involves children with undiagnosed, severe immunodeficiency problems.

According to the CDC, there have been 89 deaths associated with the MMR vaccine in the last ten years. These 89 cases, however, were not necessarily caused by the vaccine; they came from self-reported data sent in to the CDC. The Food and Drug Administration reviews all of these reports, and found no pattern in them. The causes varied substantially; in fact, there were more than 40. Some were related to serious preexisting medical conditions, like congenital heart defects, and others were completely coincidental, such as drowning and choking after the vaccine.



To put the numbers into context, the CDC's Dr. Shimabukuro said, "There have been millions of doses of MMR vaccine administered over the past 10 years. The US as a birth cohort is over 4 million, so that's millions and millions of MMR vaccines being administered."

In a separate review of adverse events related to vaccines, conducted by the well-respected medical group the Institute of Medicine, experts examined 12,000 vaccine studies. They found that the vast majority of deaths are indeed coincidental and not causally related to immunization.

The only serious adverse event they linked to the MMR vaccine was something called "measles inclusion body encephalitis," a severe brain swelling. But this seemed to happen in patients with compromised immune systems. And, as Biss explains in her book On Immunity, "We do know that 1 in about every 1,000 cases of measles leads to encephalitis, and that encephalitis has been reported after vaccination in about 1 out of every 3 million doses of the MMR vaccine."

The "absence of sufficient scientific study"

After Paul rejected, for various reasons, many of the studies that underpin the federally-endorsed vaccine schedule and the safety of vaccines, I asked him why he puts his trust in Dr. Bob above most pediatricians, researchers, the FDA, the CDC, the American Association of Pediatrics, and the World Health Organization.

"I would say that clinical judgment is what we rely on our doctors to use in the absence of sufficient scientific study," he countered. Paul and other delayers feel we just don't know enough about the safety profile of today's vaccines, and at least Dr. Bob acknowledges the uncertainty.

"It's a fact that vaccines sometimes cause bad reactions," he told me. What's more, some of the leading experts in the field — like Paul Offit — have also worked with pharmaceutical companies to develop products, and vaccine manufacturers now have former CDC officials staffing them. Though there's no clear evidence that this has led to deliberate duping or fraud, it has added to Paul's mistrust and skepticism.



"It is incredibly isolating," he said, "when you're doing something that you feel like you're using the same part of your brain that you use the rest of the day, except when it comes to this, you're crazy. And now I'm Jenny McCarthy because I'm raising concerns that Merck might not be telling the whole truth."

It doesn't seem to bother him, however, that Sears is also a businessman with a fortune to be made: a bestselling book to peddle, talks to give, products to push. Or that he's not scientist. Or that, instead of evidence delayers perceive as questionable or conflicted, Sears has no evidence at all.

Paul continued in an email, saying it's the duty of the pubic-health community to "push for further studies that allow us to validate or refine the schedule." Of course, this is undeniable.

Even a group of independent Cochrane Collaboration researchers, who reviewed the totality of the safety evidence on the MMR vaccine, pointed out that the quality of the long-term safety data wasn't very high.



They also told me that there is a good reason for this.

We don't do randomized trials on vaccines after they hit the market; it would be unethical to give half of a group of children a vaccine against a contagious disease, and leave the other half defenseless.

Pharmaceutical companies do run randomized trials on their drugs — testing for efficacy and safety — on tens of thousands of patients before they hit the market. Because these trials are relatively small, they might not reveal rare side effects that would only turn up in millions of kids, nor can it tell us about any long-term problems that may show up after a couple of years. That's why, after vaccines are approved, the CDC and the FDA rely on something called "post-marketing surveillance" to monitor safety in the general population.



The government has active surveillance safety networks, and also tracks "passive" adverse events reports sent in by physicians, manufacturers, parents, and patients. The latter are self reported, so they may represent true reactions or just coincidental health events; the government investigates the serious ones — including deaths — to find out. Without denying vaccines to some populations, this is the best data we'll have.

The Cochrane researchers told me that they have very high confidence in the MMR vaccine: "Even if the studies are not as perfect as they could be, we don't have reason to doubt its efficacy and safety."

This was something vaccine-delayer Marie acknowledged. When she was debating whether to give her son the MMR vaccine, and shared her thoughts on Facebook, one of her former professors sent her a message: he said his son was scheduled to get the MMR vaccine, but he got sick with a cold so they skipped the doctor appointment.

The next day, his son had a seizure for the first time. The professor told Marie that if he had gone to get the MMR vaccine, he would have been convinced it was because of the shot. "There are coincidences," Marie conceded, "cases where parents blame the vaccine for their autism, or kids who will have seizures anyway. But at the time my thinking is I already know my son has epilepsy, so this worries me. I'm definitely going to delay."

An emotional risk-benefit calculation

Vaccines are among the most studied and utilized medicines we have. After half a century of inoculating millions of babies around the world with routine shots, we have what should be very confidence-inducing safety information.

These shots do more good than harm. They save lives. Full stop.

Serious risks from vaccines, according to the data, are almost infinitesimally remote, and many of the popular theories about side effects — such as the MMR-autism connection — have been discredited.

We also have clear evidence that vaccines have massively improved the quality of life globally. Just look at the incredible charts on the improvements of under-five child mortality over the last century. Some of that had to do with hygiene and improved nutrition; but many of the gains had to do with these life-saving interventions. Millions of kids were suddenly no longer dying from common scourges like polio and measles.

These shots do more good than harm. They save lives. Full stop.

These facts don't dissuade the delayers, who want something science can't offer: absolute certainty and zero risk. But medicine is a play of risks and benefits. Vaccines, as we have seen, come with potential harms — but for an overwhelming benefit to public health. Maybe the problem is that today's parents mostly can't see that benefit.

I recently spoke to one parent who could: an Amish man in Ohio, which was the site of one of the largest measles outbreaks in two decades. His friends and family had been refusing the MMR vaccine after a rumor spread that it made a couple of local kids sick. All that fear about the vaccine melted away last year. Since he lived through the terrible 2014 measles outbreak, which hit more than 350 people around him, he said he and his family all got vaccinated. "After people saw how sick people got, they changed their minds."

Right now, we don't fully understand the impact of the vaccine delayers. Maybe their customized schedules won't help spread diseases. Maybe we'll even muster evidence to prove that they're right. It's unlikely that this group will cause polio to return, but what we know about the vaccine-exempt is instructive: they're much more likely to contract illnesses and the outbreaks they cause are costly. It seems likely that delayers may end up missing shots because their self-styled schedules are too demanding and that they'll leave kids unprotected for longer periods of time — for absolutely no credible reason.

In a follow-up email, Paul — a clearly thoughtful and compassionate man — said he'll continue to side with Dr. Bob until there's better evidence to disprove him. With that, he added something that's basically irrefutable. "Making medical judgments for your child or patient isn't a matter of counting the number of people on each side of the issue."

He continued: "Parents have the right to ask sincere questions in good faith, and to be given honest, evidence-based answers, not simply 'many more people feel that concern is unwarranted than not.'"