Over the years, vaccinations that help protect children from infectious diseases such as measles and mumps have saved hundreds of thousands of lives in the U.S., and prevented millions of hospitalizations, according to the Centers for Disease Control and Prevention (CDC).

But there’s so much confusing information online about vaccines for children these days that it can be tough to know what’s true and what’s not. Can vaccines really make kids sick? Should shots be spaced out as much as possible so youngsters’ immune systems don’t get overwhelmed? 

Here, some common myths about vaccines for kids—and what you need to know now.  

Myth #1: The MMR Vaccine Causes Autism

A study back in 1998 purported to link autism to the measles, mumps, and rubella (MMR) vaccine—which children typically receive at 12 months and four years of age—generating lots of headlines and fear.

But that study has been widely and soundly debunked and an overwhelming majority of experts agree that vaccines for children aren’t a factor in autism. (In fact, Andrew Wakefield, the lead author of the study was ultimately forbidden to practice medicine in the U.K., in part because he falsified the study’s findings.)

According to Wendy Sue Swanson, M.D., a pediatrician at Seattle Children’s Hospital and spokesperson for the American Academy of Pediatrics, since that erroneous study was published, numerous other studies have been conducted to examine whether there is a connection between autism and vaccines, and absolutely no connection has been found. (Get a rundown of all the medical studies about vaccines for children and autism here and more on the topic from the CDC here.)

Swanson says she understands why people might think the two are linked. The MMR vaccine is administered at the same phase in children’s lives when they may first begin to show signs of autism spectrum disorder (such as not responding when called by name, seeming oversensitive to noise, and more).

Myth #2: It’s Safer to Space Out Kids’ Vaccines

Each year, the CDC recommends a vaccination schedule for children (they do one for adults as well). This tells healthcare providers and parents when youngsters should receive vaccines for a variety of infectious diseases, such as hepatitis B, rotavirus, human papillomavirus, and tetanus.

But some people worry that having so many vaccines in a short period of time early in life—children get as many as 29 shots by age 6, not counting the yearly flu vaccine—may overwhelm kids’ immune systems. And some ask their doctors to delay vaccines or spread them out. In a 2012 survey of pediatricians by researchers in Colorado, nearly 93 percent said that in a typical month, at least one parent of a young child would ask to stretch out the vaccine schedule.

That’s unwise, says Wilbert van Panhuis, Ph.D., assistant professor of epidemiology at the University of Pittsburgh. The CDC, he says, bases the schedule on disease risks and vaccine effectiveness at specific ages, and the way vaccines may interact with each other.

“To start mixing this up is really complicated and actually can be dangerous,” he says—in part because putting vaccines off can leave kids vulnerable to infectious diseases.

The MMR vaccine, for instance, is timed so that children receive it just as they’ve lost residual immunity from their mothers.

Measles, one of the diseases that the MMR protects against, is highly contagious. If a child is unvaccinated, and comes into contact with a person who has it—or even walks into a room that person recently left—he or she has a 9 in 10 chance of contracting it, too. A child who’s had both recommended doses of the MMR has only a 3 percent likelihood of developing the measles, according to the CDC.

Though it may feel like a lot of shots for young children, each contains only tiny amounts of dead or inactive viruses or bacteria. (These help create antibodies, which spur kids’ immune systems to fight off those viruses and bacteria if they encounter them in the future.) And children come into contact with thousands of germs every day in their normal environments.

So stick to the CDC’s schedule, if you can. If your child misses a dose, not to worry: CDC makes recommendations for how to catch up. Ask your pediatrician.

Myth #3: Vaccines Can Make You Sick

Has your child ever gotten a shot and then come down with a respiratory infection?

This complaint is most common with the flu shot. Doctors often hear, “I got the flu shot and I got sick,” says Pedro Piedra, M.D., professor of molecular virology and microbiology and of pediatrics at Baylor College of Medicine.

Likely, this is a coincidence, he says. Most influenza vaccines are delivered in the fall and early winter. “That’s when we have highest rate of respiratory viruses circulating and causing mischief,” Piedra notes.

The flu shot can’t cause the flu (or another infection), but may spark some mild and temporary flu-like symptoms. This is actually a good sign, according to Swanson: it means the vaccine is effectively building immunity.

None of the other vaccines approved by the Food and Drug Administration (FDA) can cause the illnesses they protect against either. But like the flu shot, they can have temporary side effects, such as mild fever or swelling at the injection site. Get a rundown of these side effects here.

Myth #4: Vaccines Contain Harmful Chemicals

Some formulations of certain vaccinations for children contain substances that may sound worrisome, notably formaldehyde or traces of mercury.

However, according to the FDA, the quantity of formaldehyde in a vaccine is smaller than the amount that’s naturally produced by our bodies. (Some vaccines for hepatitis, flu, meningococcal disease, polio, and others may contain formaldehyde.)

When it comes to mercury, the type that’s used in some flu vaccines—ethylmercury—is quite different from methylmercury, the kind that is highly toxic and found in some seafood, Piedra notes.

Ethylmercury leaves your body within a few days, and poses no danger to children, he says. (However, in response to consumer concerns, manufacturers are phasing out the use of mercury in most vaccines altogether.)

Unless you’re allergic to one or more ingredients in vaccines, or can’t receive them for other health reasons (talk to your doctor to discuss any potential problems), the substances used to make them can’t hurt you.

Myth #5: Since Everyone Else Has Vaccinated Their Kids, I Don’t Need to Vaccinate Mine

Theoretically, if everyone in your community is up to date on vaccinations, it will help protect your family—but there’s no way to be sure that’s the case unless you’re in California. The state government there publishes vaccination rates for all schools and day care centers, but it’s the only state that does so.

It’s also important to know that for each infectious disease, a certain percentage of people in the area must be vaccinated to keep outbreaks at bay (the percentage varies from condition to condition).

While those who are unvaccinated are more likely to get sick during an outbreak, even people who are up to date on their shots are at some risk. That’s because no vaccine offers 100 percent protection.

That’s what happened in 2014 with the measles. For that year, the CDC reported 23 separate measles outbreaks—with more than 600 total cases across the country. Apart from that spike, we’ve had between 55 and 220 cases of measles in the U.S. in the past 8 years.

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