These are the facts behind the worries.

It’s natural for new parents to have questions about what they put into their baby’s body, including vaccines.

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To separate fact from fiction, BuzzFeed Life spoke to two experts, and asked them about the most common concerns new parents have about vaccinating their kids.

We talked to Dr. Kate O’Brien, pediatric infectious disease specialist and executive director of the International Vaccine Access Center at Johns Hopkins Bloomberg School of Public Health, and Dr. Jon Abramson, professor of pediatrics at Wake Forest Baptist Medical Center. Both doctors are members of the World Health Organization’s Strategic Advisory Group of Experts on Immunization, and really know their stuff. Here’s what they had to say.

Should I be worried that the measles vaccine causes autism?

In a word, no. The idea that vaccines were linked to autism came from a research paper published in a prominent scientific journal. But it turns out that the research was completely wrong — the study author, Andrew Wakefield, actually falsified his data (meaning, he made it up). The paper was retracted, and Wakefield lost his license (see more on that here). Abramson says that research shows absolutely no link between vaccines and autism.

I’ve heard that the mercury in vaccines might cause autism too. Is that true?

First, regarding mercury in vaccines causing autism: “The answer is unequivocally no,” says Abramson, who adds that many studies have confirmed this.

But something else worth mentioning: Most vaccines don’t contain mercury anymore, anyway. The measles vaccine doesn’t, for instance. “There’s a little bit of mercury in some flu vaccines — the ones made by egg,” Abramson says. But even those vaccines contain incredibly small amounts of mercury that aren’t harmful to you, he says. See more about the different types of flu vaccines here, if you want some more information.

Is There Any Reason Why A Parent Shouldn’t Vaccinate Their Child?

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Can vaccines cause multiple sclerosis?

Research hasn’t found a connection between vaccines and multiple sclerosis, either. Abramson specifically mentions a study published in the Journal of the American Medical Association in January. The study authors tracked nearly 4 million women who received the HPV vaccine, and found no causal relationship between the vaccine and multiple sclerosis rates — the percentage of women in the study who were diagnosed with multiple sclerosis during the time period was no higher than the rate of multiple sclerosis for the general population. Meaning: The vaccine and the diagnosis weren’t related.

Is it true today’s vaccinations are too much for a child’s immune system to handle all at once?

“Your immune system when you’re born starts getting exposed to many more antigens than on any day you’re vaccinated,” Abramson says. Essentially, adding one more to the tens of thousands your baby is exposed to on a regular basis isn’t going to make a difference to your kid’s immune system.

And here’s something else that might make you feel better: “The vaccines that we give now, first of all, are vaccines that are really well characterized — we understand in a lot of detail what’s in those vaccines,” O’Brien says. “And although we’re giving more vaccines than we used to, we’re actually giving fewer exposures to those kids than we did years ago before the vaccines that weren’t as specifically designed.”

Meaning: Yes, it’s more shots — but those shots are so specific that your kid is actually getting way fewer exposures than what you were personally exposed to when you were a kid. More shots, less exposure.

I’ve heard it’s actually healthier for the body to develop healthy immunities via exposure to these diseases naturally. True?

The short answer to this is no, the vaccines are a much better way to develop an immunity — they let you build an immunity without actually having to get sick.

Here’s a longer answer.

Think about chicken pox parties from your own childhood. Chicken pox is a virus that’s much more severe and dangerous in adults than it is in children, so before the vaccine existed, parents would often intentionally expose their kids to the disease, to get it over with, rather than run the risk of them not catching it as kids and then getting it as adults. And that idea made sense to a degree, Abramson says: Natural exposure to the virus made the kids sick, definitely, but it also protected them from a potentially devastating disease in their future.

THAT BEING SAID, not all kids who got the chicken pox fared well and were totally fine. For starters, it’s a miserable bug, so even without serious complications, kids still suffered and felt terrible. Even scarier, though, is that many thousands of people ended up in the hospital from chicken pox each year, and 100 to 150 people died from it annually in the United States, according to the Centers for Disease Control. And we’re talking about the early 1990s here (the vaccine came out in 1995).

The thing about diseases that we vaccinate against is that for all of them, even healthy people can sometimes develop serious complications or even die from them (like with chicken pox). So getting vaccinated is a way to train your immune system to deal with those bad bugs without having to actually go through the whole process of being sick in the first place.

“Immune systems are constantly sampling the environment that we’re in,” O’Brien says. “We’re constantly in contact with tens of thousands of germs, and it’s important for the immune system to sample those things, because that’s how the immune system matures. Giving specific vaccines so that we’re targeting the immune system to respond to certain pathogens in the future is doing more of what our body is doing on a daily basis anyway.” It’s like a chicken pox party without actually having to get the chicken pox.

Is There Any Reason Why A Parent Shouldn’t Vaccinate Their Child?

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Is it true that vaccines do in fact have side effects?

Yes, definitely. “There are potential side effects in every vaccine,” Abramson says.

Hopefully this will make you feel better, though: “I think the first important point is, all vaccines that are recommended for use have undergone extensive evaluations — both for whether they work, and also for safety,” O’Brien says. “The second thing is, the most common side effects of vaccines are mild reactions that are self-resolving [meaning, they go away on their own]. Really local reactions, and in some vaccines some low-grade fever.”

But what about the really terrifying and scary side effects you may have read or heard about? O’Brien says that extreme reactions (like allergic reactions) can happen, but they are incredibly rare (often to the tune of about one in a million — or even more). And even then, it depends on the particular vaccine. “What you’re not hearing about are the millions of doses of vaccines that are given every year when nothing bad happens,” she says.

And another thing to remember: Just because something bad happens a few days or weeks after someone was vaccinated does not mean that the vaccine caused the bad thing to happen, O’Brien says. For example, think back to that recent study about the HPV vaccine and multiple sclerosis — numerous women during the course of the study did get diagnosed with multiple sclerosis. But the percentage of diagnoses was the same as the percentage in the general population as a whole. Meaning that the vaccine date just coincidentally happened around the same time as the diagnosis — but it didn’t cause the disease.

What about people who say measles isn’t so bad that I need to worry about it?

“There are [more than] 100,000 children dying of measles globally,” Abramson says. According to the World Health Organization, 145,700 people died from measles in 2013 across the world; most of them were children.

Some people say that measles deaths and complications from the measles typically affect people who are malnourished or unhealthy to begin with, and it’s not something that people in the United States need to worry about. That’s not true. For starters, anyone with a newborn has to worry, and anyone who has a compromised immune system (cancer patients, people with immunodeficiency diseases, and more). But even healthy people in the United States can end up in the hospital with measles, Abramson says. A rash and a fever might not sound like much, but the idea of an extended hospital stay might put that in perspective. And while the death rate is low from measles, it’s definitely not zero — and that’s true for healthy people and unhealthy people alike. See to get a better idea of what we’re talking about.

If everyone else is vaccinating their kid why is it so important that I vaccinate mine?

Because vaccinations impact the community at large, and actually protect the most vulnerable people in it. A few things to know:

1. Some people can’t get vaccinated, due to medical reasons — or because they’re too young. People with compromised immune systems (cancer patients, people with genetic immunodeficiencies, and more) can’t get vaccines. And babies often can’t get some vaccines (like the measles), because their immune systems won’t actually respond to it yet. (“Nothing bad will happen, but it just won’t work,” O’Brien says. “It’ll be a wasted shot.”)

2. Vaccines aren’t 100% effective, so even people who get vaccinated could still potentially contract the disease in question.

3. HERD IMMUNITY is the idea that when enough people in a community get vaccinated against a disease, that protects the entire community (read: the vulnerable people who can’t be vaccinated). That’s because when so many people are protected, the disease just can’t spread from person to person.

4. When too many people choose not to get vaccinated, the herd immunity suffers. The babies and cancer patients are no longer protected if someone with the disease enters the community. It can spread to them — and that’s terrible, because many of these diseases are much more deadly in those populations specifically.

5. Without herd immunity, outbreaks can happen. Like what’s happening now.

Is There Any Reason Why A Parent Shouldn’t Vaccinate Their Child?

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What about people who say that vaccines pose a greater risk than the small chance of catching the disease?

“That argument is this: Since we’ve wiped out these diseases like measles, why should I take any risk?” Abramson says. “The answer is exactly what’s happening right now. When we eliminated smallpox from the world, we stopped giving the vaccine. And if we ever eliminate polio from the world, which we’re getting closer and closer to doing, we will stop vaccinating. But things like measles are not eliminated from the world. There are many, many, many thousands of children globally dying from it, and until we can eliminate it from the world there’s a risk.”

I’ve heard that vaccines don’t actually work. True?

Not all vaccines are 100% effective in every person who gets them — that’s true. The measles vaccine, for instance, is only about 95% effective. And certain vaccines can become less effective over time, which means that adults need to get booster shots to make sure they remain protected. (Measles is not one of those — the measles vaccine ought to afford you protection for life, even if you got the shot decades ago, O’Brien says).

But Abramson says that statistics show that vaccines really do work. With chicken pox, for example, the rate of hospitalizations and death have declined by 90% since the introduction of the vaccine. And just looking at actual measles cases in the United States before and after vaccines: According to the CDC, from 1953 to 1963, the United States saw an average of 549,000 cases of measles per year. Between 2001 and 2011, by contrast, the median number of measles cases in the U.S. was 62. And the WHO says that between 2000 and 2013, the measles vaccines prevented an estimated 15.6 million deaths globally. Vaccines are responsible for those astonishing decreases. Vaccines work.

Is There Any Reason Why A Parent Shouldn’t Vaccinate Their Child

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