Health Topic

Vaccines

Vaccines protect against life-threatening diseases. Follow a recommended immunization schedule to protect yourself and others at all stages of life.

Reviewed Reviewed by a registered pharmacistGeneral information

Also called: Immunization · Vaccination

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About 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 diseases caused by:

  • Viruses, like the ones that cause the flu and COVID-19
  • Bacteria, including tetanus, diphtheria, and pertussis

There are several types of vaccines:

  • Live-attenuated vaccines use a weakened form of the germ.
  • Inactivated vaccines use a killed version of the germ.
  • Subunit, recombinant, polysaccharide, and conjugate vaccines use only specific pieces of the germ, such as its protein, sugar, or casing.
  • Toxoid vaccines use a toxin (harmful product) made by the germ.
  • mRNA vaccines use messenger RNA, which gives your cells instructions for how to make a protein (or piece of a protein) of the germ.
  • Viral vector vaccines use genetic material, which gives your cells instructions for making a protein of the germ. These vaccines also contain a different, harmless virus that helps get the genetic material into your cells.

These vaccines may work in different ways, but they all spark an immune response. The immune response is the way your body defends itself against substances it sees as foreign or harmful. These substances include germs that can cause disease.

There are different steps in the immune response:

  • When a germ invades, your body sees it as foreign.
  • Your immune system helps your body fight off the germ.
  • Your immune system also remembers the germ. It will attack the germ if it ever invades again. This "memory" protects you against the disease that the germ causes. This type of protection is called immunity.

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.

Vaccines are important because they protect you against many diseases. These diseases can be very serious. So getting immunity from a vaccine is safer than getting immunity by being sick with the disease.

For a few vaccines, getting vaccinated can actually give you a better immune response than getting the disease would.

But vaccines don't just protect you. They also protect the people around you through community immunity.

Community immunity, or herd immunity, is the idea that vaccines can help keep communities healthy.

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 type of protection means that the entire community is less likely to get the disease.

Community immunity is especially important for 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.

Vaccines are safe. They must go through extensive safety testing and evaluation before they are approved in the United States.

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. Following the schedule allows them to get protection from the diseases at exactly the right time.

It sits within Infections and Immune System.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Vaccines

9,898 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

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Diagnosis and Tests

Related Issues

Statistics and Research

Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Vaccination, Immunization, Vaccines. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Vaccines, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.