What are vaccines?
Vaccines are injections (shots), liquids, pills, or nasal sprays that you take to teach your body's immune system to recognize and defend against harmful germs. For example, there are vaccines to protect against
Most vaccines contain germs (or parts of germs) that cause disease. The germs have been killed or weakened enough that they won't make you sick. But they will spark an immune response, which helps your body fight off the germs. Your immune system will also remember the germ and attack it if that germ ever invades again. This protection against a certain disease is called immunity.
The COVID-19 vaccines that are authorized in the United States work differently. They are mRNA (messenger RNA) vaccines. mRNA vaccines teach your cells how to make a protein (or just a piece of a protein) that triggers an immune response. This builds immunity and protects you from getting infected if the real virus enters your body.
What are immunization and vaccination?
Immunization is the process of becoming protected against a disease. But it can also mean the same thing as vaccination, which is getting a vaccine to become protected against a disease.
Why are vaccines important?
Vaccines are important because they protect you against many diseases. Since these diseases can be very serious, it is safer to get immunity from a vaccine than from getting sick with the disease. And for a few vaccines, getting vaccinated can actually give you a better immune response than getting the disease would.
Vaccines not only protect you; they also protect the people around you. This idea is called community immunity or herd immunity.
Normally, germs can travel quickly through a community and make a lot of people sick. If enough people get sick, it can lead to an outbreak. But when enough people are vaccinated against a certain disease, it's harder for that disease to spread to others. This means that the entire community is less likely to get the disease.
Community immunity is especially important for the people who can't get certain vaccines. For example, they may not be able to get a vaccine because they have weakened immune systems. Others may be allergic to certain vaccine ingredients. And newborn babies are too young to get some vaccines. Community immunity can help to protect them all.
Are vaccines safe?
Vaccines are safe. They must go through extensive safety testing and evaluation before they are approved in the United States.
What is a vaccine schedule?
A vaccine, or immunization, schedule lists which vaccines are recommended for different groups of people. It includes who should get the vaccines, how many doses they need, and when they should get them. In the United States, the Centers for Disease Control and Prevention (CDC) publishes the vaccine schedule.
It's important for both children and adults to get their vaccines according to the schedule. This makes sure that you get protection from the diseases at exactly the right time.
- Get Shots to Protect Your Health (Adults Ages 19 to 49) (Office of Disease Prevention and Health Promotion) Also in Spanish
- Recommended Adult Immunization Schedule for ages 19 years or older, United States, 2019 (Centers for Disease Control and Prevention)
- Vaccine Basics (Department of Health and Human Services)
- Vaccines for Adults: Which Do You Need? (Mayo Foundation for Medical Education and Research) Also in Spanish
- Vaccines.gov (Department of Health and Human Services) Also in Spanish
Diagnosis and Tests
- Screening Checklist for Contraindications to Vaccines for Adults (Immunization Action Coalition) - PDF Also in Spanish
- Community Immunity: How Vaccines Protect Us All (National Institutes of Health)
- Heart Disease, Stroke, or Other Cardiovascular Disease and Adult Vaccination (Centers for Disease Control and Prevention) Also in Spanish
- HIV Infection and Adult Vaccination (Centers for Disease Control and Prevention)
- Keeping Your Vaccine Records up to Date (Centers for Disease Control and Prevention) Also in Spanish
- Liver Disease and Adult Vaccination (Centers for Disease Control and Prevention)
- There Are Vaccines You Need as an Adult (Centers for Disease Control and Prevention) Also in Spanish
- Vaccinations and Flu Shots for People with Cancer (American Cancer Society) Also in Spanish
- Vaccinations for Adults with Diabetes (Immunization Action Coalition) - PDF
- Vaccine Safety: MedlinePlus Health Topic (National Library of Medicine) Also in Spanish
- Weakened Immune System and Adult Vaccination (Centers for Disease Control and Prevention)
- What Would Happen If We Stopped Vaccinations? (Centers for Disease Control and Prevention) Also in Spanish
- What's in Vaccines? (Centers for Disease Control and Prevention)
- Who Should Not Get Vaccinated with These Vaccines? (Centers for Disease Control and Prevention)
- Vaccine-Preventable Disease Photos (Immunization Action Coalition)
- ClinicalTrials.gov: Vaccines (National Institutes of Health)
Journal Articles References and abstracts from MEDLINE/PubMed (National Library of Medicine)
- Article: COVID-19 in the elderly people and advances in vaccination approaches.
- Article: Hepatitis B vaccination status and knowledge, attitude, and practice regarding Hepatitis...
- Article: Impact of HPV-16/18 AS04-adjuvanted vaccine on preventing subsequent infection and disease...
- Vaccines -- see more articles
Find an Expert
- Centers for Disease Control and Prevention Also in Spanish
- National Institute of Allergy and Infectious Diseases
- Travelers' Health: Destinations (Centers for Disease Control and Prevention)
- Vaccine Finder (Department of Health and Human Services)
- Shots for Safety (National Institute on Aging)