Patient education: COVID-19 vaccines (The Basics)

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What is COVID-19? — COVID-19 stands for "coronavirus disease 2019." It is caused by a virus called SARS-CoV-2. The virus first appeared in late 2019 and quickly spread around the world.

More information about COVID-19 is available in a separate article. (See "Patient education: COVID-19 overview (The Basics)".)

What are vaccines? — Vaccines are a way to prevent certain serious or deadly infections. When a person gets a vaccine, this is called "vaccination" or "immunization."

To understand how vaccines work, it helps to understand what happens when you get an infection. Infections are caused by germs, such as bacteria or viruses. When a germ gets into your body, it multiplies (makes copies of itself) and attacks, which can make you sick. Your "immune system," or infection-fighting system, recognizes that the germ should not be there. In response, it starts to make proteins called "antibodies" to fight the germ.

There are different types of vaccines. They all work by causing your body to make antibodies, like it would if you had an infection. This prepares your immune system to fight off germs if you come into contact with them in the future. Most vaccines are given as shots, although some come in other forms. Some require more than 1 dose to fully protect you from infection.

Thanks to vaccines, the number of people who die from infections has gone way down.

What are boosters? — A booster is a dose given some time (months or years) after a person first gets vaccinated. This is because the protection you get from a vaccine can decrease over time. Experts recommend boosters for some vaccines to "remind" the immune system how to protect against a specific infection.

Why should I get the COVID-19 vaccine? — Getting vaccinated lowers your chances of getting infected. If you do get infected, you will be much less likely to get severely ill if you have been vaccinated.

In addition to protecting yourself, getting vaccinated will also help protect other people, including those who are at higher risk of getting very sick or dying. It also protects people who can't get a vaccine, like young babies. Even if you are not worried about getting very sick yourself, you could still spread the virus to others, even without realizing it.

How do COVID-19 vaccines work? — Multiple COVID-19 vaccines have been developed. They work in slightly different ways.

In the US, there are several COVID-19 vaccines available. All of these have been found to work very well in preventing serious illness and death from COVID-19. They include:

●mRNA vaccines – There are 2 available "mRNA vaccines." mRNA refers to genetic material from the virus that causes COVID-19. This genetic material is used in the vaccine. It gives the body instructions to make a specific piece of protein that is normally found on the virus. In response, the immune system then makes antibodies that can recognize and attack the virus in the future.

The mRNA vaccines for COVID-19 are made by the Pfizer and Moderna companies. They come in 2 forms:

•The "monovalent" form protects against the original version of the virus.

•The "bivalent" form is similar to the original vaccines, but also protects against the Omicron variant of the virus. The Omicron variant spreads more easily than earlier versions of the virus, so the bivalent vaccine was created to give people extra protection.

●Recombinant protein vaccine – This type of vaccine contains a version of a specific protein that is found in the virus. It is combined with another ingredient to help trigger the immune system. The immune system then makes antibodies that can recognize and attack the virus in the future. Other vaccines, such as those used to prevent hepatitis B and shingles, work in a similar way.

The recombinant protein vaccine for COVID-19 is made by the Novavax company. It is available to adults age 18 years and older.

●Vector vaccine – The "vector vaccine" for COVID-19 contains a weakened version of a different virus, called an adenovirus. This virus does not make you sick, but it acts as a "vector," or a way to deliver instructions to all of the cells in your body. These instructions tell your body to make the protein that is normally found on the virus that causes COVID-19. Then, your immune system makes antibodies that can recognize and attack the virus in the future.

The vector vaccine for COVID-19 is made by the Johnson & Johnson company. It is available to adults age 18 years and older.

Different COVID-19 vaccines are available in other countries.

Which vaccine should I choose? — In the US, experts recommend getting an mRNA vaccine (Pfizer or Moderna) or a recombinant protein vaccine (Novavax). This is based on what they know about how well the vaccines work and the risk of rare side effects.

The vector vaccine (Johnson & Johnson) is still a good choice for people who cannot or choose not to get one of the other vaccines. Any of the available vaccines is better than none.

If you have a choice of vaccine and are not sure which one to get, your doctor or nurse can help you decide.

How many vaccines do I need? — This depends on your age, your health, and which vaccine you get first. (When you are vaccinated for the first time, this is called the "initial series.") The information below is for people in the US.

For adults and children age 12 years and older:

●Initial series – All of the vaccines used for the first vaccination are "monovalent." They protect against the original version of the virus. The options are:

•Pfizer – 2 doses, 3 to 8 weeks apart

•Moderna – 2 doses, 4 to 8 weeks apart

•Novavax – 2 doses, 3 to 8 weeks apart

•Johnson & Johnson – 1 dose

For people with a weak immune system, experts recommend getting an extra dose as part of the initial series for the Pfizer, Moderna, or Johnson & Johnson vaccines. An mRNA (Pfizer or Moderna) vaccine is used for this. If you have a health condition or take certain medicines that might weaken your immune system, your doctor or nurse can tell if you if you should get an extra dose.

●Booster – Experts recommend a booster dose if it has been at least 2 months since the last vaccine. A bivalent mRNA vaccine (either Pfizer or Moderna) is used for the booster, even for people who got a different vaccine originally. The bivalent vaccine is similar to the original vaccines, but also protects against the Omicron variant of the virus. This helps give extra protection when used as a booster.

For children 5 to 11 years:

●Initial series – Either mRNA vaccine can be used. The doses and timing depend on which vaccine you choose:

•Moderna – 2 doses, 4 to 8 weeks apart

•Pfizer – 2 doses, 3 to 8 weeks apart

●Booster – Children in this age group should also get a booster dose with a bivalent vaccine. The booster should be at least 2 months after the initial series. Children 5 years and older can get the Pfizer bivalent booster, while children 6 years and older can get either Pfizer or Moderna.

For children 6 months to 4 years:

●Initial series – Either mRNA vaccine can be used. Babies and younger children get smaller doses than older children and adults. The doses and timing depend on which vaccine you choose:

•Moderna – 2 doses, 4 to 8 weeks apart

•Pfizer – 3 doses. The first 2 doses are given 3 to 8 weeks apart. The third dose should be with the bivalent vaccine. It should be given at least 8 weeks after the second dose.

●Booster – For children age 6 months to 4 years, available boosters depend on which vaccine was used for the initial series:

•Moderna – Children who had the Moderna vaccine should get the Moderna bivalent booster. This should happen at least 2 months after the initial series.

•Pfizer – For children who had all 3 doses of the Pfizer vaccine, there is not yet an available booster.

If you are not sure how many vaccine doses you need, or which vaccine you should get for a booster, ask your doctor or nurse.

Can people who have been vaccinated still spread the virus? — Vaccines work very well to prevent serious illness and death, but they do not prevent 100 percent of infections. So it is still possible for a person who has been vaccinated to get COVID-19. Then, that person can spread the virus to others.

Even though you could still get COVID-19 after being vaccinated, remember that you are much less likely to get severely ill or die, especially if you have also had all recommended boosters.

Does the COVID-19 vaccine cause side effects? — It can. Temporary side effects are common, and can include:

●Pain where you got the shot (upper arm)

●Fever

●Feeling very tired

●Headache

If you get a vaccine that comes in 2 doses, side effects are more common after the second dose. They can also happen after a booster dose. While side effects can be annoying, they should not last longer than a day or 2. Some people do not have bothersome side effects at all. If you do have side effects, this does not mean that you are sick, just that your immune system is responding to the vaccine.

Vaccines also sometimes cause more serious side effects, such as severe allergic reactions. But this is rare. If you have had a reaction to the vaccine or its ingredients in the past, you might need to talk to an allergy expert. They can help you figure out if you should get the COVID-19 vaccine. People who do get the vaccine might be monitored for 15 to 30 minutes to make sure that they do not have an allergic reaction.

Other serious side effects are rare, but have happened:

●A very small number of people have developed inflammation of the heart muscle after receiving an mRNA (Pfizer or Moderna) or recombinant protein (Novavax) vaccine. This is called "myocarditis." Most cases have been in teen or young adult males. This side effect is extremely rare, and is usually mild and treatable if it does happen.

●There has been a very small number of reports of people getting blood clots after they had the single-dose (Johnson & Johnson) vaccine. Experts have confirmed that the risk of blood clots is extremely rare, and much smaller than the risk of getting very sick with COVID-19.

●A very small number of people have had a problem called Guillain-Barré syndrome after getting the Johnson & Johnson vaccine. When this happens, it causes severe muscle weakness. Experts are studying this to better understand whether it is directly related to the vaccine.

For most people, the benefits of getting vaccinated against COVID-19 are much greater than the risks. If you had a COVID-19 vaccine within the last 3 weeks, let your doctor or nurse know right away if you have any concerning symptoms. These include severe and persistent headache, blurry vision, weakness on 1 or both sides of the body, back pain, trouble thinking clearly, severe belly pain, trouble breathing, leg swelling, tiny red spots on the skin, bruising easily, or chest pain.

Can I get COVID-19 from the vaccine? — No. You cannot get COVID-19 from the vaccine.

Some people worry that the vaccine actually contains the virus that causes COVID-19. The vector vaccine that is available in the US does contain virus, but it is a different virus. It is also created in a lab in a weakened form so that it will not make a healthy person sick. mRNA and recombinant protein vaccines do not contain virus at all.

How do I know the vaccine is safe? — COVID-19 vaccines were developed very quickly. Because of this, some people wonder if they are safe. The answer is yes, the new vaccines had to go through the same process as other vaccines to test them for safety. This involved running "clinical trials" with lots of people who volunteered to try the vaccine. The volunteers included people of all ages and ethnicities. During these trials, researchers studied how well the vaccines work and how many people had side effects. The results were reviewed by doctors and other experts who do not work for the drug companies that made the vaccines. These experts agreed that the vaccines are safe and effective enough to be given to the public.

Since COVID-19 vaccines became available, billions of doses have been given. So we have a lot of information about their safety.

Do I still need the vaccine if I have had COVID-19? — Yes. Experts recommend getting vaccinated even if you had COVID-19 in the past. People who get COVID-19 do develop antibodies that likely provide some protection against getting infected again. But it is not known exactly how long antibodies last after a person recovers. Also, the antibodies that you get from a vaccine might give you stronger protection against new virus variants.

Will I have to pay for my vaccine? — No. In the US, COVID-19 vaccines are free, even if you do not have insurance. You might be asked for your insurance information, if you have it, but this does not mean that there will be a cost to you.

What if I am pregnant? — Experts have been studying the safety of the COVID-19 vaccine during pregnancy. Based on what they have learned, they recommend that pregnant people get the vaccine. Pregnant people might be more likely to get seriously ill if they get COVID-19, so getting vaccinated is especially important.

What can I do after I am vaccinated? — When you are up to date on vaccination, you are much less likely to get seriously ill if you are infected. "Up to date" means that you have gotten a vaccine plus any recommended boosters.

Some activities, like traveling to certain areas or attending certain events, require people to show proof of vaccination. Getting the vaccine will make it easier to get back to doing the things that you enjoyed before the pandemic.

If you are up to date on vaccination, you do not need to self-quarantine if you come into contact with someone who has COVID-19. But experts still recommend wearing a mask around other people for 10 days, as well as getting tested.

In many places, COVID-19 is still spreading quickly, and cases are continuing to increase. This is mostly due to virus variants that spread more easily. In the US, you can check the level of spread where you live at this website: https://covid.cdc.gov/covid-data-tracker/#datatracker-home. Most people who are in intensive care units (called "ICUs") or dying from COVID-19 are unvaccinated.

What if I have other questions? — It's normal to have a lot of questions or to be nervous about the idea of getting a vaccine that you haven't had before. Your doctor or nurse can help answer your questions or direct you to sources that you can trust.

Be careful with information you find on the internet or social media. In some cases, it can be hard to tell what is true and what is false. This is especially dangerous if people share health information that is not based on science or evidence.

You can find more information about COVID-19 vaccines through the US Centers for Disease Control and Prevention (CDC): www.cdc.gov/coronavirus/2019-ncov/vaccines/index.html.