Vaccines Explained: Types, How Immunity Works, Herd Immunity and the Schedule

A vaccine teaches your immune system to recognize a harmful germ and fight it off. Vaccines come as shots (injections), liquids, pills or nasal sprays, and protect against diseases caused by:

• viruses — such as those behind the flu and COVID-19;
• bacteria — such as tetanus, diphtheria and pertussis.

The main types

They work in different ways, but every one sparks an immune response — the body's defense against anything it sees as foreign or harmful, germs included.

What an immune response does

1. A germ gets in, and your body recognizes it as foreign.
2. Your immune system fights it off.
3. Your immune system remembers it, and will attack if it ever comes back.

That memory protects you from the disease the germ causes. The protection is called immunity. A vaccine gives you it without having to get sick first.

Immunization or vaccination?

Immunization is the process of becoming protected against a disease. It is also used to mean vaccination — getting a vaccine in order to be protected.

Why vaccines matter

• Many of the diseases they prevent can be very serious, so gaining immunity from a vaccine is safer than gaining it by catching the disease.
• For a few vaccines, the shot gives a better immune response than the disease itself would.
• They protect the people around you, too.

Community immunity

Community immunity — also called herd immunity — is how vaccines keep whole communities healthy. Left alone, germs can move quickly through a community and make many people sick, sometimes sparking an outbreak. When enough people are vaccinated against a disease, it has a much harder time spreading, and everyone is less likely to catch it.

That matters most for people who can't get certain vaccines:

• people with weakened immune systems;
• people allergic to certain vaccine ingredients;
• newborn babies, too young for some vaccines.

Are vaccines safe?

Yes. Before a vaccine is approved in the United States, it must pass extensive safety testing and evaluation.

The vaccine schedule

A vaccine (immunization) schedule lists which vaccines are recommended for which groups of people — who should get each one, how many doses, and when. In the United States, the Centers for Disease Control and Prevention (CDC) publishes it. Children and adults alike should follow it, so they are protected at the right time.

Sources

Based on "Vaccines," MedlinePlus, U.S. National Library of Medicine; a work of the United States government in the public domain.