Vaccination Facts

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Vaccinations (also called immunizations) are shots that help protect children and adults against serious and life-threatening diseases. When disease germs invade your body, your immune system reacts by creating substances called antibodies. Antibodies help fight the germs that make you sick. They also protect you from future infections by “remembering” the germs and defending against them if you become exposed again. This is called immunity.

Vaccines help you develop immunity to certain germs ahead of time—before you get sick. That’s because vaccines are made up of the same germs that cause disease, but a small, safe amount that has been weakened or killed so it won’t make you sick. Your immune system then learns to identify and attack the germs just as if you’d been exposed to them naturally. That way if you’re exposed to the infection later in life, your immune system already knows how to protect you.

Childhood Vaccinations

Immunizations are scheduled throughout childhood, many beginning within the first few months of life. By following a regular schedule and making sure a child is immunized at the right time, you’re ensuring the best defense against many diseases, including tetanus, diphtheria, whooping cough, measles, mumps, rubella, pneumonia, meningitis, influenza, and chickenpox, to name just a few. Ask your child’s doctor which vaccinations your child needs and when.

Adult Vaccinations

Although children receive the majority of vaccinations, there are many reasons for adults to stay up-to-date on vaccinations, too. First, you may not have gotten a certain vaccine as a child. Second, your immunity can fade over time. Third, new vaccines are now available. Finally, some vaccines are meant to be given regularly, such as the flu shot. The vaccines you need will depend on your risk factors and medical history. Talk with your doctor to find out which vaccines you should get.


Vaccines are considered the greatest public health achievement in the history of healthcare. Vaccines benefit both the people who receive them and the vulnerable, unvaccinated people around them by stopping the spread of infection. Vaccines also reduce the number of deaths and disability from infections.

Safety Concerns

All vaccines are fully tested before being approved for use by the U.S. Food and Drug Administration, but some people still have concerns about the safety of vaccines. For instance, some parents worry that the measles, mumps, and rubella (MMR) vaccine might cause autism. But vaccine safety experts, including the American Academy of Pediatrics and the Institute of Medicine, agree that the rise in autism rates is not due to the vaccine, and research has found no link between the two.

Side Effects

As with many medications, there is a chance that a vaccine may cause side effects. These are generally minor and will likely disappear within a few days. Examples include a sore arm or redness and swelling at the injection site. But choosing against immunization also involves risk. Most health experts agree that the benefits of vaccination far outweigh the potential risks. If you have questions about vaccines, talk with your doctor.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Apr 27
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.

  1. How Vaccines Work. Centers for Disease Control and Prevention.

  2. Vaccines (immunizations) overview. MedlinePlus, U.S. National Library of Medicine.