This article appeared in SELF. Read the full story here.

It’s a confusing time to be a parent, especially when it comes to vaccines. The internet is rife with misinformation, making it hard to separate vaccine fact from fiction. Here are some facts: Vaccines have helped to eradicate deadly diseases and keep millions of people—especially children and other vulnerable populations—safe every day. Vaccinating children born between 1994 and 2018 will prevent around 419 million illnesses, 27 million hospitalizations, and 936,000 deaths, according to the Centers for Disease Control and Prevention (CDC).

However, thanks to all the confusing falsehoods swirling around it’s understandable if you’re a parent who has some questions about vaccines. To help put your mind at ease, SELF talked to two pediatricians who specialize in infectious diseases to get answers to the vaccine questions they hear most often. (We combed through data too.)

By the way, pediatricians usually welcome these kinds of questions, so don’t hesitate to talk all of this information over with your child’s doctor.

“Parents, like doctors, are doing their best to try to weigh risks and benefits for their kid. I never mind when people go out of their way to understand the best thing for their child,” Adam Ratner, M.D., associate professor of pediatrics and microbiology at NYU Langone, tells SELF. “We’re all on the same team. We all want your child to grow up happy and healthy and not get diseases that we can avoid.”

With that in mind here are some questions pediatricians get all the time about vaccines, along with their reassuring answers.

1. What’s the point in getting vaccines if they’re not 100 percent effective?

It’s true that in an ideal world, vaccines would be 100 percent effective. In the meantime vaccines are still our first line of defense against vaccine-preventable diseases. Even though they’re not perfect, they do a pretty damn good job.

When administered according to schedule (the first dose between 12 and 15 months and a second at four through six years old), MMR vaccines are about 97 percent effective against measles, 88 percent effective against mumps, and at least 97 percent effective against rubella, according to the CDC. Likewise getting both doses of the varicella vaccine for chicken pox (which is administered on the same schedule as the MMR vaccine) is estimated to be 98 percent effective at preventing any form of chicken pox and 100 percent effective against severe chicken pox. (Apologies if this vaccine wasn’t available to you when you were a kid.)

Even vaccines that aren’t as effective are still crucial for keeping you and your family safe. The influenza (flu) vaccine, for example, was about 40 percent effective in the 2016 to 2017 and 2017 to 2018 flu seasons. That may not sound like much, but it can make a huge impact. A 2018 Proceedings of the National Academy of Sciences of the United States of America report showed that even if the influenza vaccine is only 20 percent effective, compared to no vaccine it could still prevent around 21 million infections or illnesses, 130,000 hospitalizations, and 62,000 deaths. That’s even if only 43 percent of the population gets it (which is roughly how many U.S. adults get the flu vaccine each year).

And very few things in life are 100 percent effective, especially when it comes to health and safety, but that doesn’t mean they’re worthless. Think of vaccines as if they were seat belts, Aaron Milstone, M.D., pediatric epidemiologist and associate professor of pediatrics at the Johns Hopkins University School of Medicine, suggests. “Seat belts aren’t 100 percent effective in preventing death in a car accident,” he tells SELF. But you’re probably still all about seat belts for your child because the added safety just in case is very much worth it.

2. Is it possible for vaccines to make someone sick with the illness they’re supposed to prevent?

Almost never, says Dr. Ratner. In most cases it’s not even biologically possible.

Some vaccines (such as for polio) are comprised of inactivated or “killed” antigens (parts of germs that cause the body’s immune system to build disease-fighting antibodies), according to the CDC. This means they can’t cause disease. Instead they use the dead germ to teach your child’s immune system to mount a response so if they did encounter the real thing, they’d be better at fighting it off, according to Dr. Ratner.

Other vaccines only contain specific parts of the germ in question, such as its protein, sugar, or the casing around it, says Dr. Ratner. An example is the hepatitis B vaccine. Because these vaccines don’t have whole, live antigens, it’s impossible that they’d be able to cause those illnesses.

In the vast majority of cases kids can’t even contract illnesses from live, attenuated vaccines. These types of vaccines contain weak yet living versions of the disease in question; unlike the actual disease you’d encounter in the wild, though, the amount present in the vaccine is very small—small enough that your children’s immune systems can typically handle it without an issue. Injecting a live virus to prevent your child from getting sick from that very same virus sounds kind of scary, but researchers have spent a significant amount of time testing the safety and efficacy of vaccines, determining that as a broad rule even live vaccines aren’t going to make people sick. That said, in some rare cases these live vaccines will create mild immune responses that mimic the symptoms you might have with the disease itself (which might be why some people believe that vaccines give you the actual disease). With the varicella vaccine, for instance, there is a small chance—3 percent after the first dose and 1 percent after the second dose, according to the CDC—that a child will develop a limited rash that resembles a mild form of the chicken pox. But this is simply a part of the immune response to the vaccine and isn’t the same as actually getting sick with the chicken pox. And the even better news is that after getting vaccinated, the child would be protected from the more serious, naturally occurring form of the virus.

The only feasible way a live, attenuated vaccine can cause the disease it’s meant to prevent is if your child’s immune system is compromised for some reason, like if they have certain health conditions that affect the immune system (such as HIV) or if they’re on immune-suppressing medications (such as chemotherapy or immunosuppressive therapy), says Dr. Milstone. Usually you and your child’s doctor will already be aware of that and decide not to administer any live, attenuated vaccines.

Also worth noting here: Vaccines don’t work immediately. How long they take to become as effective as possible varies, but in general it can be a few weeks, the CDC says. It’s possible that your child could catch an illness they just got vaccinated against in that time (like the flu during flu season), which would wrongly make it seem like they got sick from the vaccine.

3. Can my baby’s immune system handle the recommended vaccination schedule or multiple vaccines at once?

Yes. Parents often worry that vaccines will leave a baby’s immune system vulnerable, like it will be too busy mounting a response to an immunization to deal with any other illnesses. Luckily that’s not how it works. Your baby might seem defenseless, but their immune system is not a delicate flower, says Dr. Ratner. Plus vaccines only contain a tiny fraction of the antigens your baby normally encounters on a daily basis.

“Vaccines are just a drop in the bucket compared to the loads of bacteria and viruses that kids are exposed to day to day,” says Dr. Ratner. “When we give vaccines all that we’re doing is giving the immune system a head start [in] developing the antibodies it needs to fight off a small group of very dangerous diseases.”

The above still applies if your child is getting multiple vaccines at once. Even then their immune system can handle it. You can read more about why that practice is safe (and why you should follow the immunization schedule) here.

4. What are the possible side effects of vaccines?

As with any medication, vaccines can cause some side effects. Most of them are minor, such as pain, swelling, or redness at the injection site, or a low-grade fever, the CDC explains. It definitely isn’t fun to see your kid dealing with these types of symptoms, but they typically go away within a few days.

The chance of a serious reaction to a vaccine such as a severe allergic reaction is extremely low. This kind of thing is estimated to happen with fewer than one in a million vaccine doses, the CDC says. Doctors are trained to respond in the very unlikely case of a reaction, with tools like epinephrine and oxygen on hand.

Vaccines can also cause mild fevers as a normal part of their intended immune response. Very rarely these fevers can lead to short seizures that don’t cause any lasting harm, the CDC explains. These are known as febrile seizures and they’re very unlikely to happen in connection with vaccines. They only affect at most about 30 of every 100,000 vaccinated children, according to the CDC. What’s more, they can happen with anything that causes a fever, including illnesses that vaccines help to protect against.

Febrile seizures can occur with even a mild temperature increase, but they’re most likely to happen in kids who are six months to five years old with a fever of 102 degrees Fahrenheit or higher, the CDC says. Febrile seizures can also happen when a child’s temperature is going down.

You might be wondering if there’s a way to prevent febrile seizures, for instance by giving your child ibuprofen or acetaminophen to bring down their fever. It’s a good question, but as of now there’s no way to prevent febrile seizures. (Remember, although febrile seizures look frightening they don’t cause children any permanent harm.) It’s typically OK to give children six months and older who have fevers at or over 102 degrees this type of medicine to reduce their temperature, but since these seizures can happen at any point in a fever (even as it’s going away) and at any heightened temperature, these meds won’t eliminate the seizure possibility. (Which, again, is rare.)

Doctors urge parents not to avoid vaccination because of the extremely unlikely chance of something like a severe allergic reaction or febrile seizure. “There’s no medicine, no intervention, that anyone can say never has any risk associated with it,” says Dr. Ratner. “The decision not to vaccinate is associated with risk too.”

5. Why do kids need to be immunized if a disease has been eliminated?

The reason certain diseases have been eliminated in the United States is because of vaccines. We understand that it can be hard to see the threat in diseases that seem more suited to a history book than reality, but vaccines are what put those diseases in the past—and keep them there.

As we’ve seen with the recent measles outbreaks, if enough people don’t vaccinate against something it can come back. Thanks in large part to an effective nationwide measles vaccination program, this disease was declared eliminated from the United States in 2000 (meaning there hadn’t been continuous disease transmission for over a year), the CDC explains. Fast forward to 2019 and there have been over 1,100 measles cases confirmed in 30 states, mostly in communities with many unvaccinated people.

“That is in large part driven by parents making that decision [not to vaccinate],” says Dr. Ratner. “They think, ‘We don’t see measles here anymore, why would I take any risk?’ And the response is: You are taking a risk by not getting vaccinated.”

Lower vaccination rates reduce herd immunity. Herd immunity happens when a large enough proportion of a community is vaccinated against something so that if a certain disease is introduced into the community it will have a hard time spreading. Even if a vaccine-preventable disease is uncommon or eliminated in the United States, it might still be common in other parts of the world. An unvaccinated child traveling to those areas or people from those areas visiting your community could leave the child susceptible to diseases.

This goes back to the seat belt metaphor. “You don’t wear your seat belt because you think you’re going to get into a car accident every time you drive,” says Dr. Milstone. “You wear your seat belt because if you get into a car accident, you want to be as protected as you can be.”

6. Why is the vaccine schedule updated so frequently?

Definitely not. For starters, by the time an immunization winds up on the vaccine schedule at all, it has gone through a ton of safety testing. “It can take decades from someone developing a candidate vaccine in a lab to that vaccine going into clinical trials and then finally becoming part of the recommended immunization schedule,” says Dr. Ratner. These tests make sure the vaccine is safe not only by itself, but also in combination with other vaccines that are already on the schedule.

With that in mind, year-to-year changes don’t generally reflect safety data. The changes you see are typically refinements of safe vaccines to make them more effective, or the introduction of a new, even more effective formulation, according to Dr. Ratner. For example, in 2006 the Advisory Committee on Immunization Practices (ACIP) recommended a second dose of the varicella vaccine at age four to six years in addition to the dose around one year, based on research that showed that immune responses to the chicken pox vaccine seemed to wane over time.

Circling back to the whole car safety thing: Think of how updated car models come out every year. A newer, fancier model doesn’t automatically mean that older ones are suddenly obsolete or dangerous.

7. Are vaccines linked to autism?

Short answer: No. Long answer: Absolutely not. There is no relationship between vaccines and autism, according to the CDC, the mounds of research done on this topic, and both the experts we consulted.

“The hypothesis of a link between vaccines and autism was originally raised by an unethical paper that was done by a doctor who lost his license for good reason,” says Dr. Ratner, speaking of a long-debunked, now-retracted 1998 study that incorrectly suggested the MMR vaccine was increasing autism in British children. This study has since been thoroughly discredited because of procedural errors, its tiny sample size of 12 kids, and serious ethical violations, like making the child subjects undergo invasive testing without parental approval and accepting funding from lawyers who were representing parents involved in lawsuits against vaccine manufacturers.

According to Dr. Ratner, one of the reasons this myth persists is because the first dose is given around one year of age, which is within the age range when symptoms of autism may become apparent. However, experts have identified symptoms of autism that can be recognized earlier than one year, long before they have received that vaccine. And even if a parent does first notice autism symptoms after their child gets a vaccine, that doesn’t mean the vaccine caused those symptoms, as the CDC explains.

It’s also completely unfounded that thimerosal (a preservative that contains mercury) in vaccines might be a cause of autism. Nine CDC-funded or conducted studies published in or later than 2003 have found no link here.

Not only has data from many studies shown no evidence of harm caused by the very low doses of thimerosal in vaccines, but thimerosal was never even in the MMR vaccine, the CDC says. It has also never been in some other common childhood vaccines, like varicella, inactivated polio, and pneumococcal conjugate vaccines (that last one protects against bacteria that can cause illnesses like pneumonia).

Beyond that, since 2001 thimerosal has not been included in any other routine vaccinations for children six and under (like DTaP to protect against diphtheria, tetanus, and pertussis), except in the most minute trace amounts due to manufacturing, the Food and Drug Administration (FDA) explains. The only exception is the inactivated influenza vaccine, the FDA says, which still contains a very small amount of thimerosal overall. There are also thimerosal-free formulations of the influenza vaccine, the CDC says. (But the CDC and similar public health organizations have not recommended avoiding vaccines with thimerosal for any reason.)

Moreover, since this effort has taken place to reduce or eliminate thimerosal in vaccines, the autism rate hasn’t gone down, the CDC says. It’s actually increased, which underscores that vaccines do not cause autism.

Numerous researchers have studied this and continue to reach the conclusion that there is no connection between vaccines and autism.

8. Is there ever a reason to get vaccines early or ahead of schedule?

This question pops up mostly around vaccines that are recommended when a child hits a year old, Dr. Ratner says, like the MMR inoculation. The first dose is recommended at 12 months, as opposed to vaccines recommended earlier than that, like the hepatitis B vaccine (recommended at birth) and the first dose of the DTaP vaccine (recommended at two months). Is it possible and safe to get vaccines earlier than recommended for maximum protection?

Yes, under some circumstances. “If a parent is traveling with their child where they may be exposed to measles, then we might recommend they get the vaccine as early as six months of age,” says Dr. Milstone. (You can check out this list of recent measles outbreaks if you’re traveling within the United States, and the CDC recommends the MMR vaccination before any international travel.)

In fact many routine childhood vaccinations have minimum ages that are slightly earlier than their recommended ages, according to the CDC—for instance the minimum age for the first dose of DTaP is six weeks while the recommended age at first dose is two months. So why not just get vaccines as early as possible if it’s safe to do so? There is some research to suggest that getting vaccinated before the suggested schedule could be less effective in some way, at least in the short-term.

All in all, if and when your child can get an early vaccination will be a case-by-case situation, so talk it over with their pediatrician for more information.

9. What if I can’t afford to get my child vaccinated?

Both Dr. Ratner and Dr. Milstone emphasize that your child’s doctor will likely be more than happy to help you find free or affordable vaccination options.

“Pediatricians want kids to be healthy, and we spend a lot of time teaching parents how to do that and pointing them towards resources,” says Dr. Ratner.

Vaccinations are generally cheaper—or even free—at a public clinic or health department versus at a private physician’s office. Through the federally-funded Vaccines for Children (VFC) program, your child might qualify for free vaccinations at these types of centers and participating doctors’ offices if they are Medicaid-eligible, uninsured, under-insured (meaning your insurance doesn’t cover any or all vaccines), or American Indian or Alaska Native. Here’s where you can find a local VFC coordinator to answer any questions you might have.

10. What happens if I choose not to vaccinate my child?

Doctors strongly advise against this. “When you choose not to vaccinate, you’re choosing to potentially expose your child to serious but preventable diseases,” says Dr. Milstone, not to mention potentially exposing other people in your community who rely on herd immunity to stay healthy.

“Think of vaccines as a gift you can give your kids,” says Dr. Milstone. “Driving them to baseball practice is nice, giving them presents on their birthday is thoughtful, but giving them a vaccine can save their life.”