Understanding the Why, Who, and When of COVID-19 Vaccines

Understanding the Why, Who, and When of COVID-19 Vaccines

This article is for anyone who wants to learn more about COVID-19. The goal of this patient education activity is to help patients and their care partners talk to their doctors about COVID-19 vaccines and engage in shared decision-making.

You will learn about:

  • COVID-19 and conditions that could put you at a higher risk for severe illness

  • How you build immunity

  • How COVID-19 vaccines protect you and why they're important

  • Getting the COVID-19 vaccine

  • Questions to ask your doctor or pharmacist

Medicines listed in this activity have either a US Food and Drug Administration (FDA) approval or have been given an Emergency Use Authorization (EUA) by the FDA to treat or prevent COVID-19.

The information on COVID-19 is continually changing. The content in this activity is accurate based on the information that was available at the time of its publication. This resource is provided for educational and informational purposes only. We do not provide medical advice, diagnosis, or treatment. 

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COVID-19: The Basics

COVID-19 is caused by a type of virus called a coronavirus. Exposure to the virus can cause an infection that usually starts in your upper respiratory tract (nose, sinuses, and throat). Because this specific coronavirus is new (novel) and we haven't been exposed to it before, COVID-19 is a new disease for humans.

COVID-19 is thought to spread mainly by droplets in the air that form when someone who's infected talks, coughs, or sneezes. The virus can then infect someone else when these droplets enter their mouth, nose, or eyes.

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COVID-19's Impact on Your Body

Most people with COVID-19 have mild or no symptoms. But for some, COVID-19 can be severe and even deadly.

COVID-19 can damage many different organs and systems in your body. This can lead to symptoms and complications (additional problems) that can be long lasting.

Anyone can get COVID-19, but it is especially dangerous for elderly people. Being pregnant, smoking, or having certain medical conditions could also put adults, of any age, at a higher risk for severe illness.

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Conditions That Could Put You at a Higher Risk for Severe Illness

Conditions that could put you at a higher risk for severe illness from COVID-19 include:

  • High blood pressure

  • Certain heart or blood vessel conditions

  • Diabetes

  • Obesity or being overweight

  • Certain lung conditions, such as moderate to severe asthma or chronic obstructive pulmonary disease (COPD)

  • Chronic (long-term) kidney disease

  • Liver disease

  • Cancer

  • Certain nerve and brain conditions, including dementia

  • A weakened immune system

This is not a full list of conditions. Talk to your doctor to see if you may be at a higher risk of severe illness from COVID-19.

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How Your Body Builds Immunity

Your immune system -- your body's natural defense system -- is made up of different organs, cells, and proteins that work together to protect you when you're exposed to an outside invader, such as the virus that causes COVID-19.

When you're exposed, your immune system is triggered and makes proteins called antibodies to attack the invader and fight off infection. It can take several days or weeks for antibodies to develop. But they stay in your body and can recognize and defend against the invader if you're exposed to it again. This helps give you protection (immunity) against a future infection.

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How Vaccines Help Protect You

Vaccines have been used for hundreds of years to help protect us against many different diseases. Unlike medicines that treat a disease after it happens, vaccines are given before an infection to try to prevent disease.

Once given, a vaccine triggers your immune system to make antibodies. This can give you immunity against a future infection without actually having to get the disease first.

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Why Are Vaccines for COVID-19 Important?

Because COVID-19 can cause long-term damage and be life-threatening, it's important to be protected against getting it and spreading it to others. A vaccine is a safer way to help build immunity than getting the disease. Even if you feel healthy, you run the risk of severe illness and complications from COVID-19.

The vaccines currently being used for COVID-19 have an Emergency Use Authorization (EUA) from the FDA, the US agency that makes sure medicines are safe and effective. A vaccine may get an EUA when the known and potential benefits of using it outweigh the known and potential risks.

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Who Can Get the COVID-19 Vaccine?

Currently, the COVID-19 vaccine may be used in people 18 or 16 years of age and older, depending on which vaccine is used. The vaccines should not be given to anyone who has had a severe allergic reaction -- called anaphylaxis -- to any part of the vaccine.

Our nation's public health agency -- the CDC (Centers for Disease Control and Prevention) -- has made recommendations about who should get the vaccine first, such as elderly people. Each state also has its own plan for deciding who will get the vaccine first and how people can get it.

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When Can You Get the Vaccine?

Talk to your doctor or pharmacist or check your local health department's website for information about getting the COVID-19 vaccine. Your age and any medical conditions you have may be important factors in determining when you can get it.

If you have COVID-19 symptoms, you should wait to get the vaccine until you're fully recovered and you've finished the necessary self-isolation.

If you've had COVID-19, you should still get the vaccine. That's because it's not yet known how long you're protected after having COVID-19. If you had COVID-19 treatment, talk to your doctor about how long you should wait before getting the vaccine.

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Questions to Ask Your Doctor or Pharmacist

Questions you can ask your doctor or pharmacist about getting the COVID-19 vaccine can include:

  • Where can I get the vaccine?

  • What vaccines are available?

  • If I have or had COVID-19, can I still get the vaccine?

  • Are there any side effects from the vaccine?

  • How long after my last shot will I be fully protected?

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You have successfully completed the program Understanding the Why, Who, and When of COVID-19 Vaccines.

View Additional Materials

View Additional Materials on this topic that you may find useful:

CDC's COVID-19 Vaccine Rollout Recommendations

Frequently Asked Questions About COVID-19 Vaccination

COVID-19 Vaccine Information for Specific Groups

COVID-19 and Older Adults

People With Certain Medical Conditions

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Authors and Disclosures

Clinician Reviewer

Susan L. Smith, MN, PhD

Senior Director, Learning & Development, Medscape, LLC.

Disclosure: Susan L. Smith, MN, PhD, has disclosed no relevant financial relationships.


Anita A. Galdieri, PharmD, RPh

Associate Medical Education Director, Medscape, LLC.

Disclosure: Anita A. Galdieri, PharmD, RPh, has disclosed no relevant financial relationships.


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