Vaccines are a crucial part of contemporary medicine. This is for everyone who is not yet convinced of the necessity to get your shots.

What follows is a list of those vaccine-related dangers which were found to be statistically significant. Be aware that even though you might have these increased risks, they are still negligible in comparison to the immunity that the shot gives you, and the people around you.

≈ moderate certainty of an increased risk = high certainty of an increased risk

MMR* ≈ Transient pain in a joint (rubella component, only women)

  • ≈ Transient pain in a joint (only children)
  • = an acute allergic reaction
  • = Febrile Seizures1
  • = Measles Inclusion Body Encephalitis (measles, only individuals with demonstrated immunodeficiencies)


  • = an acute allergic reaction
  • = Varicella2


  • ≈ Oculorespiratory Syndrome3
  • = an acute allergic reaction
  • = an acute allergic reaction (only yeast-sensitive individuals)


  • ≈ an acute allergic reaction

DT–, TT–, and aP– Containing tetanus toxoid

  • = an acute allergic reaction


  • = an acute allergic reaction

If you are not convinced, or just interested, read the following excerpts from a conversation between Sam Harris and Dr Nina L. Shapiro:

  • Shapiro: some private schools in Los Angeles and Orange County have vaccination rates similar to those of countries in sub-Saharan Africa. This is true of affluent areas in northern California as well, such as Marin County. Then there was an outbreak of measles, a disease that had once been declared eradicated in the US, which came courtesy of a happy congregation of unimmunized people at Disneyland. This story also became national news, and measles has now spread to at least 17 states.
  • Shapiro: One is that they haven't seen these illnesses. Most people with young children have never seen a case of measles; they've never seen mumps, rubella, polio, or whooping cough; so these illnesses are just abstractions to them. Their families are healthy, so why should they worry about something they've never seen?
  • Shapiro: And there's the concern that these vaccines cause autism. No matter how many studies are done to show in hundreds of thousands of children that there is no association between immunizations and the development of autism, there's still that inkling of fear. Because most people know what autism looks like. They don't know what measles looks like, but they understandably want to do everything they can to prevent autism.
  • Shapiro: notion that vaccines have what people call "toxins" in them. This is a very tricky word, because most non-scientists don't really know what a toxin is. Vaccines are not toxic. The air we breathe is much more toxic than the vaccines that children receive. They receive more viral and bacterial exposure just by being outside for a few hours than they would from vaccines.
  • Harris: The carefree attitude we now enjoy is the result of the success of vaccines. This is why people are no longer dying of smallpox. So we live in a world that has been more or less purged of terrifying, preventable illness because we have used vaccines for generations. Bliss leads to ignorance. People have the luxury of ignoring "herd immunity" (a concept we will talk about) once it has been provided by their neighbors.
  • Harris: Another factor is that people are often confused about scientific and statistical reasoning. Even doctors can fail to reason scientifically, and a few prominent pediatricians are failing egregiously to give their patients rational advice about vaccines.
  • Harris: It's no fun watching your toddler writhe under the pediatrician's needle and then howl with pain, and the idea that you might be imposing a risk of injury or death on her in the process is horrible to contemplate. Even when, in reality, you're imposing much less risk than you often do just for fun. Which is more of a hazard to your child's health—all the potentially life-saving vaccines she'll ever receive, or that ski trip you take as a family each year? The time on skis, clearly. But it doesn't feel that way.
  • Shapiro: But if you look at pictures of kids from the 1950s lining up to receive vaccines, you'll often see that their faces are calm. They're not crying. They're not running away. They're actually standing patiently in line without their parents. But in photographs from the past 10 years—even in the literature advocating for the necessity of vaccines—you see screaming children and sad-looking parents physically restraining them. I think there's been a societal shift, regardless of what's in these needles. We now assume that children should not feel pain for any reason.
  • Shapiro: A mild risk from vaccines, which we see relatively frequently, is fever. A lot of kids who get vaccines will have a fever a few days later, and that's not to be written off as nothing, because it is quite disconcerting when a two-month-old, a four-month-old, or a six-month-old has a high fever. In extremely rare cases children have had seizures, with or without an associated fever. The chicken pox vaccine can, on rare occasions, trigger an episode of chicken pox—either a mild case, where the patient gets a little chicken pox mark right at the injection site, or a severe one. The chicken pox vaccine is usually given at age 12 months or so, and for a 12-month-old baby to have a severe case of chicken pox is serious.
  • Harris: There is even something called the Vaccine Injury Compensation Trust Fund, set up in 1988, which provides compensation for those who are harmed by vaccines, whether they belong to a vulnerable population or not. However, the people who are significantly harmed in this way appear to number in the hundreds at most, and often fewer, among the millions who receive vaccines each year. Compare this with the risk of dying from using nonsteroidal anti-inflammatories—aspirin, ibuprofen, and so forth. Here we should perceive a much greater danger. These over-the-counter medications kill 3,000 to 16,000 of us outright each year. And not necessarily from overdoses.
  • Harris: All interventions present some risk of injury or death, and because we're talking about the behavior of millions and millions of people each year, you can always find some terrible story about some unlucky person who died or was severely injured by what is, in fact, a very low risk behavior.
  • Harris: So, while we have to admit that vaccines are not without risk, the risk is lower than for interventions that most people consider trivial and wouldn't hesitate to employ, and lower than for genuinely risky lifestyle choices that many of us make.
  • Harris: Getting one's risk tolerances aligned with reality is something that could cure a lot of these fears.
  • Harris: People hear about "whooping cough" (pertussis) and think, It's just a cough. What's the big deal? Well, here is what it looks like for an infant to have this cough. If you decline to get your kids vaccinated against pertussis, they can spread this virus to infants who are too young to be vaccinated. About 20 infants die this way in the U.S. each year. People also assume that measles is more or less benign—just a rash and, perhaps, a fever. I recently came across a touching letter written by Roald Dahl, the famous children's book author, about his daughter who died of measles. She died in 1962, but he wrote this letter5 in 1986 as a public service announcement. Here is how it starts:

Olivia, my eldest daughter, caught measles when she was seven years old. As the illness took its usual course, I can remember reading to her often in bed and not feeling particularly alarmed about it. Then one morning, when she was well on the road to recovery, I was sitting on her bed showing her how to fashion little animals out of coloured pipe-cleaners, and when it came to her turn to make one herself, I noticed that her fingers and her mind were not working together and she couldn't do anything. "Are you feeling all right?" I asked her. "I feel all sleepy," she said. In an hour, she was unconscious. In twelve hours she was dead.

  • Shapiro: I think people believe that if their children are otherwise healthy and contract one of these illnesses, they'll be strong enough to fight it. But that's not always the case. Dahl's child was seven. We're not talking about an infant. She was a healthy child at the time. It doesn't necessarily matter how healthy or how old you are once you get one of these illnesses.
  • Shapiro: we are human, but we are also animals that live in herds. And depending on the effectiveness of a vaccine and the degree of contagiousness of the corresponding illness, a certain percentage of people in a community need to be immunized to protect everybody. It's not necessarily 100%, although that's obviously the goal. But for measles, for instance, 92% to 94% of a community needs to be protected to protect the remaining members who cannot be immunized—because they're either too young or immunocompromised in some way. With this level of vaccination, if the disease enters that community, those who are not immunized still have some protection. So it really is a matter of public responsibility. And so many people are now relying on the immunity of the herd that there is no longer a herd. Some school communities have a 20% immunization rate—so 80% of people are unprotected. There's no herd there.
  • Shapiro: Generally speaking, the herd depends on greater than 90% to 95% immunization for all of us. It creates a web of protection. When you are immunized for all these illnesses, the herd gets that much stronger.
  • Harris: The only reason anti-vaxxers are in a position to even entertain the possibility of not immunizing their children is that there is still so much herd immunity. These people cannot reasonably hope that everyone will stop using vaccines—that is, unless they hope to return to a world where people get paralyzed by polio because they shook another person's hand. If you decline to get your child vaccinated because you fear that vaccines may cause autism, say, you are relying on your neighbors to keep your children safe by imposing this unconscionable risk of autism on their  children. So it's not a defensible ethical position, even if we were to grant that vaccines imposed a significant risk of complications. In order to follow the advice of some of these pediatricians who recommend that you not vaccinate or that you delay specific vaccines, you're relying on those who don't follow that advice to keep your kids safe. But of course the real ethical problem is that by avoiding vaccines, you are putting everyone's children, and especially your own, at risk of contracting dangerous and entirely preventable diseases.
  • Harris: Just to be clear about the issue of autism: While we acknowledged that all vaccines have some associated risks, an increase in the incidence of autism associated with the MMR vaccine does not appear to be among them. All the research suggests that there is no link between autism and MMR, and yet the fear that there is, born of Andrew Wakefield's fraudulent study, is still burning brightly in affluent, liberal, well-educated communities. This shows how difficult it is to correct for misinformation once it has spread.
  • Shapiro: The problem is that autism is more readily diagnosed at about the time that the measles vaccine is given—anywhere from 12 months to 18 months, sometimes a little bit later. … So, yes, children will be diagnosed a month or two after they have their MMR vaccine, but it has nothing to do with the vaccine.
  • Shapiro: Working in academic medicine, we would never get away with that sort of thinking. We poke fun at anyone who says "in my experience"—because that means one case. "Time after time after time" means just three cases. When a doctor in a boutique practice in a lovely neighborhood says, "I've never seen a case of measles," anyone working in a major medical center will just roll his eyes. It's a statistical illusion. He's living in a bubble of health, which is fortunate. But it gives no indication of what's going on in the real world.
  • Harris: When you send your kid to school unimmunized, you are putting at risk someone in the school, or someone's relative at home, who can't get immunized for a real reason. Apart from the health of one's own child—which is really best protected by getting the recommended vaccines—it is this cascade of effects that one should worry about.
  • Shapiro: "I've made this decision for my family. This is best for my family." But your family doesn't live in a bubble. Your family lives in a community, and you have to have some level of social responsibility.

Sources and further reading

Source archive

  1. Most are back to normal within sixty minutes of the event. ↩︎

  2. Disseminated Oka VZV / Vaccine Strain Viral Reactivation ↩︎

  3. Inflammation in the eye, and swelling of facial skin. Resolves within 48 hours. ↩︎