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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 United States and prevented millions of hospitalizations, according to the Centers for Disease Control and Prevention.

But 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 their immune systems don’t get overwhelmed?

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

Myth: The MMR vaccine causes autism.

A study published in 1998 purported to link autism to the measles, mumps and rubella (MMR) vaccine, which children typically receive at 12 months and again at 4 years of age.

That study has since been widely and soundly debunked, and numerous other studies have found no connection between autism and vaccines. An overwhelming majority of experts now agree that vaccines aren’t a factor in autism.

Wendy Sue Swanson, a pediatrician at Seattle Children’s Hospital and a spokeswoman for the American Academy of Pediatrics, says she understands why people might think the two are linked. The MMR is administered at the same time in children’s lives as when they may begin to show signs of autism spectrum disorder, such as not responding when called by name and oversensitivity to noise.

Myth: It’s safer to space out kids’ vaccines.

The CDC’s vaccination schedule for children spells out when youngsters should receive vaccines for a variety of infectious diseases.

Some people worry that so many vaccines in a short time early in life — children can get up to 29 shots by age 6, not counting the yearly flu vaccine — may overwhelm kids’ immune systems.

So some parents request that doctors delay or spread out vaccines. That’s unwise, says Wilbert Van Panhuis, an assistant professor of epidemiology at the University of Pittsburgh. The CDC, he says, bases the schedule on disease risks, 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. The MMR vaccine, for instance, is timed so that children receive it just as they’ve lost residual immunity from their mothers. And measles, one of the diseases that the MMR protects against, is highly contagious.

Myth: Vaccines can make you sick.

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

The flu shot can’t cause the flu, though, and getting sick soon after receiving a flu shot is probably a coincidence, he says. Most influenza vaccines are delivered in the fall and early winter. “That’s when we have the highest rate of respiratory viruses circulating and causing mischief,” Piedra notes.

The shot may spark some mild and temporary flulike symptoms, a sign, says Swanson, that the vaccine is effectively building immunity.

None of the other vaccines approved by the Food and Drug Administration can cause the illnesses they protect against, either. But they can have temporary side effects, such as a mild fever or swelling at the injection site.

Myth: Vaccines contain harmful chemicals.

Some vaccines 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 naturally produced by our bodies.

As for mercury, ethylmercury — the type used in some flu vaccines — is quite different from methylmercury, which 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. (But in response to consumer concerns, manufacturers are phasing out 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, the substances used to make them can’t hurt you.

 Copyright 2017, Consumer Reports Inc.

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