Vaccines: Myth Versus Fact

There are many common myths about vaccines. In an age where misinformation spreads quickly and immunizations are part of political arguments, it’s easy to lose sight of what’s true and what is hearsay.

If you find yourself wondering if vaccines are safe and effective, here is some evidence-based information about common vaccine myths and facts offered to clear up any confusion.

Myth: Vaccines don’t work.

Fact: Vaccines are extremely effective.

Vaccines completely eliminated smallpox and has nearly eliminated many other serious diseases, such as polio, a serious respiratory illness that severely affects children.

Sometimes, people still get sick with a disease that they’ve gotten vaccinated for. This is by far most common for diseases that mutate rapidly, like the flu and COVID-19. However, getting vaccinated can still help you avoid more serious illness than if you had not been immunized.

Myth: There are dangerous ingredients in vaccines

Fact: Vaccines don’t contain full-strength germs or ingredients that can harm you.

In reality, vaccines are mostly water. Some vaccines contain a pretend version of an infection, others contain just part of a virus or bacteria, and others contain a weakened version of a germ. None of these are dangerous vaccine “ingredients” or “chemicals.”

Myth: Vaccines are unregulated and untrustworthy

Fact: Medical organizations constantly monitor the safety of vaccines and respond to safety concerns, including sharing information with the public.

We trust the rigorous process that all vaccines go through before they’re approved, and we expect more research. In the meantime, we are confident in recommending childhood vaccines to our patients.

Myth: Natural immunity is just as good as vaccination

Fact: Vaccines provide better immunity because you don’t have to get sick with a disease to build that immunity.

Many preventable diseases are dangerous and can have lasting impacts. It’s much safer—and less of a disruption to your routine—to get vaccinated instead. Plus, being vaccinated helps keep you from spreading the disease to people around you who haven't been vaccinated or might have a higher risk of serious harm from a disease.

Myth: Vaccine side effects are severe

Fact: Some side effects can be common with vaccines, but serious side effects are rare.

Your doctor may tell you to expect minor side effects, but the benefit of getting immunized outweighs any potential harm. Common side effects include pain, redness and swelling near where you got the shot, a low-grade fever of less than 100.3 degrees, a headache or a rash.

Severe side effects of vaccines are rare. If you have a severe issue after getting a vaccine, tell your doctor right away.

Myth: Vaccines cause autism

Fact: There is no evidence that vaccines cause autism.

This myth started in a single study from more than 25 years ago that turned out to have used some made-up “research.” The study was later discredited by its own authors and has also been proven false by additional researchers.

In truth, scientists have found multiple genes that are linked to autism, which would mean children with autism have had it since birth. Timing might be what makes vaccines and autism seem related. Some children start to show signs of autism around the same age they get the vaccine for measles, mumps and rubella.

Myth: You can’t get vaccinated when you’re pregnant

Fact: You can and should get vaccines when you’re pregnant.

The CDC recommends the vaccine for diphtheria, tetanus and whooping cough during pregnancy. If you’re pregnant during flu season, you should get the flu vaccine, too.

These vaccines can protect the adult and the baby. The immunity passes along to babies in the womb and can last for a few months after they’re born. This is especially important because newborn babies don’t have fully developed immune systems. If they get sick, it can become very serious.

Because vaccines before birth protect babies for only a few months after they’re born, it’s also important your baby gets all the vaccines your doctor recommends.

Myth: Declining a vaccine for my child is only a personal decision

Fact: Choosing not to get your child vaccinated is a decision that doesn’t just affect you and your child.

Not vaccinating your child has an impact on your entire community. When many people have immunity to a disease, that protects people who aren’t or can’t be vaccinated. This is called herd immunity. If not enough people are vaccinated, deadly diseases like measles can return.

Myth: I don’t have to tell anyone if I don’t vaccinate my child

Fact: If you choose not to vaccinate your child, you need to tell certain people.

These include your doctor and other medical professionals, so they can properly care for your child if they get sick. Your child’s daycare, babysitter or other caretakers should also know.

Vaccines are also required for your child to attend school in all 50 states—except for rare exceptions—and to join after-school activities or sports. Plus, vaccinations are legally required for some travel.

The American Academy of Family Physicians (AAFP) recommends immunizing all children, adolescents and adults using the AAFP recommendations unless you have certain allergies or illnesses. Talk to your doctor about any conditions you have.

Myth: Vaccines alter your DNA

Fact: Vaccines do not change or interact with your DNA in any way.

It’s impossible. All vaccines work by giving your cells information they use to start building their own protection against the virus that causes COVID-19 or other diseases. No vaccines, not even mRNA or viral vector vaccines, rewrite your DNA when they do that.

Myth: mRNA vaccine technology is untested

Fact: The technology used to develop mRNA vaccines is not new.

Researchers have studied mRNA vaccine technology for years, including for cancer research and for infections such as Zika, the flu and HIV. This long history of research helped scientists use the technology quickly when COVID-19 broke out.

Myth: COVID-19 vaccines were developed too fast

Fact: COVID-19 vaccines moved quickly because scientists around the world worked together with urgency and funding—not because anyone cut corners or skipped steps.

In 2020, the Trump administration launched “Operation Warp Speed” to speed up development of COVID-19 vaccines. Even with that fast timeline, the clinical trials for COVID-19 vaccines followed the same strict standards as for other vaccines, and many independent panels of scientists reviewed the data before any vaccine was authorized.

Myth: Vaccines exist to deliver microchips

Fact: COVID-19 vaccines do not contain microchips.

Vaccines are developed only to fight disease, not to control, influence or track anyone. Vaccines work by stimulating your immune system to make antibodies, exactly like it would if you got the disease. After getting vaccinated, you build immunity to that disease without being exposed to a dangerous amount of the disease first.

Myth: COVID-19 vaccines are linked to higher miscarriage rates

Fact: This claim is not true. The COVID-19 vaccine is not linked to higher miscarriage rates. In fact, pregnant patients who received the COVID-19 vaccine had healthier pregnancies than those who didn't.

Researchers from the Yale School of Medicine published a study analyzing COVID-19 vaccines and miscarriage rates in 2025. They didn't find any association between any of the COVID-19 vaccines and a higher risk of miscarriage. Additionally, research shows that contracting COVID-19 itself during pregnancy is associated with higher risk for preterm delivery, neonatal intensive care admission and more. That's why physicians especially recommend the COVID-19 vaccine if you're pregnant or planning to become pregnant.

The Myths and Misconceptions content is supported by an unrestricted grant from Merck Sharp & Dohme Corp.