Vaccine safety: Answers to 6 common questions

Vaccines have been used for decades to protect people against preventable infectious diseases like smallpox, polio, measles and whooping cough. The Centers for Disease Control and Prevention (CDC) estimates that 472 million illnesses were prevented through the vaccination of children born between 1994 and 2021.

While vaccines are the best defense against certain diseases, you may have questions about vaccines and vaccine safety.

Here are answers to six common questions about vaccines:

1. What are vaccines?

Vaccines help your immune system fight infections faster and more effectively. They are made of small amounts of weak or dead germs. When you get a vaccine, it sparks your natural immune response, helping your body fight off and remember the germ so it can attack it if the germ invades again. Vaccines provide long-lasting immunity to serious diseases without the risk of serious illness.

2. Do vaccines work?

Before a vaccine is recommended for use in the U.S., the Food and Drug Administration (FDA) ensures it works and is safe.

Since vaccines were invented, the number of people who get sick or die from vaccine-preventable diseases has dropped significantly. Childhood illnesses and deaths in the U.S. also have decreased significantly due to vaccines given in childhood.

3. Are vaccines safe?

All vaccines must be approved for licensing by the FDA before they can be used. FDA regulations for the development of vaccines help ensure their safety, purity, potency and effectiveness. Before a vaccine can be approved, highly trained FDA scientists and doctors evaluate the results of studies on the safety and effectiveness of the vaccine, and inspect vaccine manufacturing sites. These evaluations follow extensive testing by a vaccine's manufacturer.

The FDA also requires that vaccines undergo three phases of clinical trials with human subjects before they can be licensed for use. After the vaccine is licensed, the FDA and CDC continue monitoring it for safety.

The U.S. has the safest vaccine supply in its history, according to the CDC. Its long-standing vaccine safety system ensures vaccines are as safe as possible. Learn more about how the vaccine safety process works.

4. Is natural immunity better than vaccination?

A natural infection might provide better immunity than vaccination, but serious risks exist. For example, a natural chickenpox, or varicella, infection could lead to pneumonia or encephalitis, a serious brain infection. A natural polio infection could cause permanent paralysis. A natural mumps infection could lead to deafness. A natural chickenpox or measles infection in a pregnant woman could lead to the development of serious congenital disabilities in her unborn baby or even to a miscarriage. Vaccination can help prevent these diseases and potentially severe complications.

5. Who do vaccines protect?

Vaccines don't just protect you. They also protect the people around you.

Germs can quickly travel through a community and make many people sick. If enough people get sick, it can lead to an outbreak or a pandemic. But when enough people are vaccinated against a disease, the germs can't travel as easily from person to person, and the entire community is less likely to get the disease.

That means even people who can't get vaccinated, such as those with weak or failing immune systems, will have some protection from getting sick. And there's less chance of an outbreak or pandemic because it's harder for the disease to spread.

For example, measles spreads through the air when a person infected with the disease coughs or sneezes. According to the CDC, measles is highly contagious, and 9 out of 10 people exposed to an infected person could become infected if not protected through vaccination.

6. Do vaccines have side effects?

While vaccines can cause side effects, most are rare, mild and short-lived. In rare cases, a vaccine can cause a serious problem, such as a severe allergic reaction. Via the Vaccine Adverse Event Reporting System, the CDC and FDA track serious reactions and events related to vaccines. This is a national early-warning system to detect possible vaccine safety issues in the U.S. Anyone can report an event to the Vaccine Adverse Event Reporting System, including patients and healthcare professionals. This information is used to ensure vaccine safety in the U.S.

Talk to your healthcare team if you have questions or concerns about vaccines.

Lisa Hayes, M.D., is a physician in Family Medicine in Waseca, Minnesota.