There's no denying that immunization programs have had a major impact on disease. Before the vaccine era, the Center for Disease Control estimates that more than half a million children became sick with measles—a serious and potentially fatal illness—each year. By 2010, that number had dropped to only 61 cases—a reduction of more than 99 percent. Some conditions, like polio and diptheria, had been even more drastically reduced, and smallpox had been completely wiped out.

However, the spate of measles outbreaks in 2014 and 2015—including the recent Disneyland outbreak—demonstrate that even though we've taken huge steps to fight infectious disease, immunizations are still necessary. (The majority of the people affected by these recent outbreaks were unvaccinated.)  And despite the overwhelming success of vaccination, many parents worry about the decision to vaccinate—often because of vaccination myths that aren't always based in reality.

  • Vaccines cause autism. This theory is at the heart of many parents' decision not to vaccinate. In recent years the media has focused on anecdotal evidence connecting the onset of autism with the immunizations children receive at around 18 months to two years old. It sounds alarming, but Ari Brown, MD, FAAP, pediatrician and author of the Baby 411 series, says that "numerous studies worldwide have looked at this question and have overwhelmingly shown that this is not true." Brown says that these studies have thoroughly reviewed the schedule of vaccines, the MMR combination vaccine and specific ingredients—and found no link to autism.
  • Vaccines have dangerous ingredients. Parents and doctors alike used to think that thimerosol—a type of preservative used in vaccines—could expose children to an unhealthy level of mercury because it contains ethylmercury, a molecule containing a mercury atom. Ethylmercury has not been found to bioaccumulate (build up in the body) and is flushed out of the body much faster than methylmercury—the "bad" mercury, which can be found in foods like canned tuna fish. Regardless, today's vaccines contain only tiny traces of thimerosal, which the American Academy of Pediatrics says will cause nothing more than minor redness at the injection site, and Brown says its use in vaccines shows no connection to autism.
  • Vaccines aren't necessary anymore; we've wiped out the diseases. "I wish that were true!" says Brown. Just because we don't see huge numbers of children suffering from a disease doesn't mean it's been fully eradicated. Instead, think of the illness as lying in wait. Once you stop vaccinating in large numbers, the disease would quickly recur, quickly travelling between unvaccinated children. The recent measles outbreak at Superbowl 2012, the 2010 whooping-cough outbreak in California—which affected thousands—and the HIB meningitis outbreak in the past few years are just some of the events Brown mentions that remind us just how necessary vaccines are.
  • It's better to have a chickenpox party than get the immunization. Brown says "chickenpox and 'party' is an oxymoron—it's no party to have chickenpox." In recent years the general population has become complacent about diseases. This laissez-faire attitude's probably a result of the vaccination program working so well—we worry less about our kids getting a dangerous disease. Chickenpox in particular is often dismissed as a less serious condition, and parents who would prefer their child to develop natural immunity hold "pox parties" to purposefully expose their little one to the disease. But before you write off chickenpox as an insignificant illness, remember—it can be fatal. According to Brown, 100 deaths per year were due to chickenpox before the vaccine was introduced in 1995. Even if your child avoids the 'pox as a kid, if she's not immunized, she's vulnerable later in life—and catching it as an adult is much more severe. Brown encourages parents to consider the "extremely safe and very effective" vaccine instead, saying chickenpox "is not a disease you want your child to have, and to knowingly GIVE it to your child is a very poor parenting decision."
  • Other children are immunized, so mine doesn't need to be. AIDS and cancer patients with weakened immune systems and babies too young receive rely on the phenomenon of herd immunity for protection. A simplistic explanation of herd immunity suggests that a few unvaccinated children will be protected if all the other kids are vaccinated—but the number of immunized children must be very high for herd immunity to be effective. As parents delay or refuse vaccinations, the number of immunized children decreases to the point where herd immunity no longer exists. Brown says "you can't hide in the herd when the herd isn't protected," mentioning that like-minded parents who opt out of vaccines tend to send their children to the same preschools, playgroups and schools, creating "hot pockets" for the disease to spread.
  • There's no need to vaccinate so early—we can wait. You may have heard other parents talk about delaying the vaccination schedule, but Brown says this is a risky decision—"like waiting for six months to put your baby in a car seat, anticipating that you won't get into a car accident." Just like driving on the road, you can't control all the factors that could cause an accident—or in this case, an exposure to a potentially harmful sickness.

When it comes to vaccinations, sorting fact from fiction is essential. Check with the AAP, CDC or your pediatrician if you have questions about what you hear. Above all, remember that vaccines are designed to keep your child healthy, and are the best protection a parent has against infectious diseases.