Everything you need to know about the COVID-19 vaccines available now

Last updated: Feb 15, 2023

Learn how the four approved shots stack up and how they can help keep you safe.

Bottles of vaccines


When the first COVID-19 vaccines came out in December 2020, it was a breakthrough moment in the pandemic. Since then, nearly 225 million Americans have been fully vaccinated against COVID-19. That’s according to the Centers for Disease Control and Prevention (CDC).

Not only that, 50% of adults have gotten the first booster dose. And as of March 2022, everyone age 50 and older became eligible to get a second booster shot.

Now updated boosters from Moderna and Pfizer have been authorized by the U.S. Food and Drug Administration (FDA). (Visit My Turn to learn how to schedule yours.)

Here’s the latest look at how the COVID-19 vaccines and boosters work.

The mRNA vaccines: Pfizer and Moderna

How do they work?
The goal of any vaccine is to teach your immune system what a particular germ looks like. If the real virus or bacteria enter your body later, your immune system will know how to fight them off. Traditional vaccines use inactive or weakened germs to trigger this kind of response.

The Pfizer and Moderna vaccines for COVID-19 take a different approach. They do not contain any part of the coronavirus. Instead, they use a type of genetic material called messenger RNA – or mRNA – to deliver a set of instructions to your cells. This blueprint tells your cells to start making spike proteins if you’re exposed to the virus.

These spikes look just like the ones on the actual coronavirus. The spike proteins are harmless. But when your immune system sees them, it starts producing antibodies to fight them off.

This is the way your immune system learns what the coronavirus looks like and how to attack it. If you’re exposed to the real coronavirus later, your body will know exactly what to do to prevent you from getting sick.

Once the mRNA instructions are delivered, your cells break them down and dispose of them. The messenger RNA has absolutely no contact with your own DNA and does not change it.

How many doses are required?
Here are the current recommendations from the CDC:

For Pfizer:

  •  Adults get two doses, three to eight weeks apart.
  • Children 12 to 17 get two shots, three to eight weeks apart.
  • Children 5 to 11 get two doses, three to eight weeks apart.
  • Children 6 months through 4 get a series of three shots.

For Moderna:

  • Adults get two shots, three to eight weeks apart.
  • Children 6 months to 11 get two doses, four to eight weeks apart.
  • Children 12 to 17 get two doses, four to eight weeks apart.

Children get a smaller dose of these vaccines than teens and adults. Children and adults are considered fully protected two weeks after the second dose of either vaccine.

Are they effective?
Yes, very. Both the Pfizer and Moderna vaccines have been shown to be highly effective in preventing infection.

Earlier findings showed that the shots work well in people of different ages, genders, races, and ethnicities. And they’re safe and effective for most people with underlying medical conditions.  

Scientists are still learning how well the vaccines work against new variants. According to the CDC, the shot might work against some variants but could be less effective against others. Pfizer and Moderna have come out with updated boosters. They are designed to protect against recent Omicron variants.

On very rare occasions, mRNA vaccines have appeared to trigger anaphylaxis. This is a severe and treatable allergic reaction. It happens in only 2 to 5 people per million vaccinations. To be safe, the CDC requires that people with a history of severe allergies be watched for 30 minutes after getting the shot.

There’s also a small risk of myocarditis (an inflamed heart muscle) and pericarditis (inflamed tissue surrounding the heart) after mRNA vaccines. This rare event occurs most often in adolescent and young adult males. It usually happens within seven days of getting a second dose of Pfizer or Moderna.

You should get medical help ASAP if you have chest pain, shortness of breath, or a pounding heartbeat after you get vaccinated. That’s the recommendation of the FDA.

The protein subunit vaccine: Novavax

How does it work?
Novavax is the newest vaccine option in the U.S. The FDA approved it in July 2022. Protein subunit vaccines contain spike proteins of the COVID-19 virus.

The Novavax vaccine pairs these with an “adjuvant.” This is an ingredient that helps your immune system respond to those proteins. Then your immune system starts pumping out antibodies. This vaccine does not use any live virus, per the CDC.

How many doses are required?
Adults and children 12 to 17 receive two shots, three to eight weeks apart. It’s not authorized for children under 12.

Is it effective?

Yes. In trials, the Novavax vaccine was about 90% effective at preventing mild infections, according to the FDA. It offered 100% protection against moderate or severe cases.

There were rare cases of heart inflammation. Symptoms occurred within the first 20 days after vaccination. You should get medical care ASAP if you notice chest pain, shortness of breath, or a pounding or fluttering heart.

The viral vector vaccine: Johnson & Johnson

Viral vector vaccines use a modified version of a different virus to give your cells instructions. The Johnson & Johnson COVID-19 shot for adults 18 and up uses an adenovirus. This is a type of virus that causes the common cold.

This “vector” has been changed so that it can’t replicate and make you sick. Once the vector enters your cells, it starts churning out harmless spike proteins. Your immune system spots them and makes antibodies. 

However, the Johnson & Johnson shot is no longer considered a preferred vaccine by the CDC. That’s due to a risk of blood clots after vaccination. This vaccine is now recommended only if you can’t get one of the other vaccines.

For example, you may have had an allergic reaction to a Pfizer or Moderna shot. Or you don’t have access to any of the three other COVID vaccines.

What are the routine side effects from COVID-19 shots?
The common side effects of the four vaccines include:

  •  Pain at the injection site
  • Headache
  • Fatigue
  • Muscle aches
  • Nausea

Most side effects are mild and last a day or two.

What to know about booster shots

Booster shots are the best way to extend the protection you got from the vaccine and prevent illness.

The CDC now recommends updated boosters for people ages 5 and older. These new shots from Pfizer and Moderna are called “bivalent” boosters. This means they cover the old variants as well as the newer Omicron BA.4 and BA.5 variants.

The new booster is a single shot given at least two months after a previous vaccine or booster shot. People who have gotten more than one of the original “monovalent” boosters should also get the updated booster shot, says the CDC.

The bottom line
Vaccines and boosters protect you from getting very sick or even dying from COVID-19. Keeping up to date with your shots is one of the most important steps you can take to protect yourself. If you’re unsure about which vaccine to get, talk to your doctor.

The information in this story is accurate as of press time and posting. Staying up to date with your COVID-19 vaccines is one of the best ways to limit the spread of the coronavirus. This includes getting booster shots such as the new bivalent booster when applicable. It’s also important to wear a mask indoors in public when the infection level is high in your area. According to the CDC’s latest guidance, respirator masks (such as an N95 mask) provide the most protection. If you are at high risk of getting sick, keep your distance from others and avoid crowded places. Because the situation surrounding COVID-19 continues to evolve, we encourage readers to follow the news and recommendations for their own communities by using the resources from the CDC, WHO,their local public health department, and our COVID-19 member site.

We updated some language in this section because CDC has updated booster guidance since we sent B1. 


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