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The COVID-19 Vaccine

This article was last reviewed on June 21, 2022.

With more and more COVID-19 vaccines being approved throughout the world and many in clinical trials, it can be hard to keep up with what’s what. We’re keeping this page updated regularly to help you stay informed.

Why COVID-19 vaccination is important

COVID-19 vaccines are approved after a team of scientific and medical experts have looked at all the trial data. This must show that the vaccines are safe and effective at preventing COVID-19. Then it can be mass-produced and distributed for external use.

Getting vaccinated not only protects you, but also the people around you. This is particularly important for people at high risk of severe illness.

Based on latest evidence, the CDC is expressing a clinical preference for people to get an mRNA COVID-19 vaccine (Pfizer-BioNTech or Moderna) over the Johnson & Johnson’s COVID-19 vaccine at this time. But those who are unable or unwilling to get an mRNA vaccine will still have access to Johnson & Johnson’s COVID-19 vaccine.14

Getting vaccinated is a great way to help your body build an immune response against COVID-19 without having to experience illness.

COVID-19 vaccination is an important step to ending the pandemic

We’ve also answered some COVID-19 vaccine myths over on our COVID-19 vaccine myth-busting page.

Information on who can get a vaccine

According to the CDC, everyone 6 months of age and older is now eligible to get a COVID-19 vaccine.

More information on CDC Vaccines for COVID-19

Information on booster dose

Who should get a booster dose?

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The CDC recommends that everyone 5 years and older should get a booster shot.

When should you get a booster dose?

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Go to CDC's COVID-19 booster tool to determine if and when you or your child is eligible for a booster dose.

Why is a booster dose recommended?

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A booster dose will help better protect people against severe disease.

Which vaccine should you get as a booster?

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Those aged 18 years and older are recommended to get one of the mRNA COVID-19 vaccines as a booster shot. 5 to 17 year olds should receive the Pfizer-BioNTech vaccine as a booster shot.9

What are the risks of a booster dose?

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There is limited data at this time on the risks of receiving additional doses of these vaccines. The reactions so far are the same as were reported with the initial doses of the vaccines and the CDC and FDA are continuing to monitor the safety of all the COVID-19 vaccines.

Speak to your healthcare provider if you have questions or concerns regarding the booster dose for COVID-19.

How to find a vaccine

If you have been currently recommended to get a vaccine, try the following to find a vaccine provider near you

  • Check
  • Contact your state or local health department
  • Contact your local pharmacy or check their website
  • Text your zip code to 438829
  • Call 1-800-232-0233

Is the COVID-19 Vaccine Effective?

The science behind vaccination

The immune system

It’s helpful to start with some information about how the immune system works. Your blood contains red blood cells that deliver oxygen to the body, and white blood cells or immune cells, which fight infection.

You have many different types of specialized white blood cells. Some recognize foreign invaders, and fight them off as a first line of defense. This is called the innate immune system. The name for any foreign invader, such as such a virus, is an antigen.

You also have other white blood cells that take longer to activate, but recognize and fight specific antigens. This is called the humoral immune system. This system remembers the shape of these antigens so that if you come across that same antigen again, you can fight it off.

The main cells that protect against specific antigens and maintain this memory are B cells and T cells. B cells produce proteins called antibodies that attack the virus particles themselves. T cells attack the cells of our body that have already been infected.

How vaccines work

Generally speaking, vaccines work by helping our bodies develop immunity without being infected.

Vaccines mimic an infection. This stimulates your immune system to recognize and make a memory for the harmful antigens, without making you sick.

Sometimes after a vaccine, you may have short-lived symptoms such as a fever. This doesn’t mean you have the infection. It’s a sign that your immune system is releasing chemicals to prepare itself for what it thinks is an infection. So it’s a sign that your immune system is working.

It usually takes 2 weeks after vaccination for your body to build immunity against the COVID-19 virus.

COVID-19 vaccine and pregnancy

The CDC strongly recommends all women who are pregnant, thinking about getting pregnant or breastfeeding to get vaccinated.

For those who are pregnant or have been recently pregnant, there is an increased risk for severe illness from COVID-19.

The vaccines are safe and effective. There is no evidence currently that the COVID-19 vaccines cause any fertility problems in men or women. Current data suggests that the benefit of COVID-19 vaccine outweighs any known or potential risks during pregnancy.10

The COVID-19 vaccine types currently approved for use in the US

There are many different vaccines and vaccine types being produced and researched. We’ve taken a closer look at the ones currently approved for use in the US.

1. Genetic vaccine/nucleic acid vaccine (e.g. the Moderna and Pfizer/BioNtech vaccine)

These vaccines contain genetic material - either RNA or DNA - to give your own cells instructions to make the antigen, or part of it. For COVID-19 vaccines, this is often the spike protein, which is on the surface of the virus.

Once the RNA or DNA gets into the cell, your cells’ protein factories make the antigen that will trigger an immune response.

The injected RNA or DNA doesn’t stay in your cells. Your cells break it down.

T and B cells build an immunity to the newly created COVID-19 antigen. Since your own cells make the antigen, in large quantities, the immune reaction is strong.

Both the Moderna and Pfizer/BioNtech vaccines use mRNA to deliver the instructions for the COVID-19 antigen.

2. Viral Vector vaccines (e.g. the Johnson & Johnson vaccine)

These vaccines contain a weakened version of a live, unrelated virus, called a viral vector. The vector delivers part of the target virus’s genetic material. For COVID-19, this genetic material codes for the spike protein. This is not enough of the virus to make you sick.

Then, just as with a natural infection, your cells use the genetic code of the virus spike to make many copies of the spike protein. Your B and T cells can then mount an immune response against these.

If you later come across the real COVID-19 virus, your immune system recognizes the spike protein and is ready to fight it off.

It’s important that the viral vector is one that not a lot of people would have been previously exposed to. If we had already been exposed to it, our immune system would attack the vaccine vector before the vaccine could work.

Viral vector vaccination mimics a real infection. But the important difference is that the target virus can’t replicate.

Scientists have used this type of technology before in humans, such as for the Ebola vaccine.

Summary of vaccines


Name: BNT162b2

Type of vaccine: mRNA

Manufacturer: Pfizer, Inc., and BioNTech

It has FDA approval for people aged 16 years and older and is marketed under the brand name Comirnaty.

The Pfizer-BioNTech COVID-19 Vaccine has FDA authorization for ages 6 months to 15 years of age.

Number of shots: 2 shots, a minimum of 21 days apart

How well it works: 95% effective at preventing lab-confirmed COVID-19 illness in people aged 16 years and older without evidence of previous infection.

The Pfizer-BioNTech pediatric COVID-19 Vaccine has been shown to be 90.7% effective in preventing COVID-19 in children 5 through 11.12


Name: mRNA-1273

Type of vaccine: mRNA

Manufacturer: ModernaTX, Inc.

It has FDA approval for people aged 18 years and older and is marketed under the brand name Spikevax.

It is authorized for use in children aged 6 months - 5 years.

Number of shots: 2 shots, a minimum of 28 days apart

How well it works: 94.1% effective at preventing lab-confirmed COVID-19 illness in people who received two doses who had no evidence of being previously infected.

There have been reports of cases of heart inflammation (called myocarditis and pericarditis) after mRNA covid vaccination. These reports have been rare and mostly seen in young males age 16 years and older. In most of these cases, there has been improvement with medication and rest.8

Johnson & Johnson / Janssen3

Name: JNJ-78436735

Type of vaccine: viral vector

Number of shots: 1

It has emergency use authorization for people aged 18 years and older.

How well it works: 66.3% effective at preventing lab-confirmed COVID-19 illness in people who had no evidence of previously being infected.

The CDC has indicated a preference for Pfizer-BioNTech or Moderna COVID-19 vaccines over the Johson & Johnson /Janssen COVID-19 vaccine.

There were reports of a rare adverse event, involving blood clots with low platelets, called thrombosis with thrombocytopenia syndrome (TTS). It is contraindicated to administer the Johnson & Johnson / Janssen COVID-19 vaccine to anyone with a history of TTS after receiving Janssen or other adenovirus vector-based COVID-19 vaccines. Talk to your healthcare provider about other vaccine options for which this risk has not been seen.11

There have also been reports of a rare disorder called Guillain-Barré Syndrome (GBS) where your body’s immune system damages your nerve cells and causes muscle weakness and sometimes paralysis. Most people fully recover but some have permanent nerve damage.

These cases have been mostly reported in men aged 50 years and older.11

Who should not get a COVID-19 vaccine

You should not get vaccinated if you have any of the following:

  • If you have had a severe allergic reaction) or even an immediate allergic reaction that wasn’t severe, to any ingredient in one of the vaccines, you should not get that particular vaccine. Check with your healthcare provider if you may still be able to get a different COVID-19 vaccine.
    • A severe allergic reaction would be one where you needed to be treated with epinephrine (EpiPen) or needed to go to the hospital
    • An immediate allergic reaction would be symptoms such as hives, swelling or wheezing/trouble breathing that occurs within 4 hours of getting vaccinated
  • If you have had a severe or immediate allergic reaction to the first dose of a COVID-19 vaccine, you should not get a second dose of that vaccine.
  • If you developed TTS after receiving the Johnson & Johnson / Janssen COVID-19 vaccine or other adenovirus based COVID-19 vaccine, you should not get additional doses of the Johnson & Johnson / Janssen COVID-19 vaccine


  1. CDC Pfizer-BioNTech COVID-19 Vaccine Overview and Safety
  2. CDC Moderna COVID-19 Vaccine Overview and Safety
  3. CDC Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety
  4. The Advisory Committee on Immunization Practices’ Interim Recommendation for Use of Pfizer-BioNTech COVID-19 Vaccine
  5. The Advisory Committee on Immunization Practices’ Interim Recommendation for Use of Moderna COVID-19 Vaccine
  6. The Advisory Committee on Immunization Practices’ Interim Recommendation for Use of Janssen COVID-19 Vaccine
  7. CDC Recommends Use of Johnson & Johnson’s Janssen COVID-19 Vaccine Resume
  8. CDC COVID-19 Myocarditis
  9. Interim Clinical Considerations for Use of COVID-19 Vaccines
  10. COVID-19 Vaccines While Pregnant or Breastfeeding
  11. Selected Adverse Events Reported after COVID-19 Vaccination
  12. FDA Authorizes Pfizer-BioNTech COVID-19 Vaccine for Emergency Use in Children 5 through 11 Years of Age
  13. CDC Expands Eligibility for Booster Dose
  14. CDC Endorses ACIP's Updated COVID-19 Vaccine Recommendations | CDC Online Newsroom | CDC

The information provided is for educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Seek the advice of a doctor with any questions you may have regarding a medical condition. Never delay seeking or disregard professional medical advice because of something you have read here.