Viral vector COVID-19 vaccine fast facts

• The vaccine is approved for adults ages 18 and older. The vaccine is given as a shot in a muscle in your upper arm.

• In most cases, the mRNA COVID-19 vaccine (Pfizer or Moderna) is preferred over the J&J vaccine for both the first vaccination and boosters. Talk with your healthcare provider to learn more.

• Adults should preferably receive 2 doses of the vaccine initially. People with a weak immune system may need an extra dose. A booster is advised several weeks after. Booster advice may change depending on data about COVID-19 variants. Follow your healthcare provider's instructions about your risk and when to return for your booster.

• The viral vector vaccine does not use live, dead, or weak COVID-19 virus.

• The vaccine will not give you COVID-19.

• The vaccine will not make you sick with another virus.

• Side effects of the vaccine such as body aches and fever mean your immune system is working. It does not mean that you have the virus.

What does the viral vector COVID-19 vaccine do?

This COVID-19 vaccine has been shown to help prevent moderate to severe COVID-19 illness and the need for hospital care. If you get the virus after you get the vaccine, it may help your symptoms be milder. You are less likely to need time in the hospital. The COVID-19 vaccine may also help protect people around you from getting the infection.

COVID-19 vaccines may also lead to more widespread changes. The more people who get the COVID-19 vaccine, the less likely the virus will be able to spread in the community.

Should I get a COVID-19 vaccine?

The most important thing to do is talk with your healthcare provider. Several vaccines are available to prevent COVID-19 and reduce the severity of illness if you get the virus. No vaccine is ever 100% effective in preventing any illness, but the COVID-19 vaccines work well and are safe. The viral vector vaccine (J&J) is approved for adults age 18 or older, including people who are pregnant or breastfeeding. Several other COVID-19 vaccines are approved for children as young as 6 months. Research is being done to learn about how safe and how well the viral vector vaccine works in children. Talk with your healthcare provider about which vaccine is advised for you and your family.

People who have had COVID-19 may still be helped by the vaccine. Researchers don’t yet exactly know how long natural immunity lasts after you have COVID-19. Your healthcare provider may advise you to get vaccinated if you had COVID-19 more than 90 days ago.

Tell your healthcare provider if you have ever had a severe allergic reaction to food or medicine. Talk with them about your risks if you carry an epinephrine autoinjector. This may affect your provider’s advice to you about the vaccine.

How does a viral vector COVID-19 vaccine work?

Researchers make this vaccine with a viral vector. This means they use another type of virus to carry instructions into your body’s cells. The virus is an adenovirus. This is a very common type that causes colds. For the J&J vaccine, adenovirus type 26 (Ad26) is used. But this virus has been changed so it can’t reproduce in your cells or cause illness. This means you can’t get a cold from the vaccine. Instead, it has been given instructions to tell your cells how to make a harmless piece of a protein called a spike protein.

A spike protein is found on the outside of the SARS-CoV-2 virus that causes COVID-19. Your immune system sees this spike protein as a threat, and creates antibodies and other defenses against it.

After the spike protein is found and attacked by your immune cells, the instructions and the viral vector are destroyed. Antibodies and immune cells against the spike protein of SARS-CoV-2 are now part of your immune system.

This will help your body's immune system recognize and fight the real SARS-CoV-2 virus if it ever shows up. It’s kind of like recognizing someone by the hat they wear. Your body is then prepared to spot COVID-19 and fight it off before it grows in your body’s cells.

How was this COVID-19 vaccine approved for safety?

The COVID-19 viral vector vaccine has passed many tests in labs and in tens of thousands of people, and meets strict standards from the FDA. It has also been given to millions of people around the world since the initial studies were completed.

The vaccine was tested first in animals. It was then tested in a series of clinical trials that included thousands of people. All of the data from these tests was collected and submitted to the FDA and other scientific groups. These committees of scientists and public health experts carefully look at the data to see if a vaccine is safe and effective. If the vaccine meets the FDA's strict standards of safety and quality, the agency tells the vaccine company they can make the vaccine for emergency use.

How much does the vaccine cost?

The U.S. government is providing the vaccine free to U.S. residents. But the site where you get your vaccine may bill a fee to your health insurer for giving you the vaccine. Talk with your health insurer, local pharmacy, employer, or healthcare provider to find out more about a possible fee. You can’t be denied a vaccine if you don’t have health insurance or can’t pay the fee yourself.

Getting the viral vector COVID-19 vaccine

The vaccine is given as a shot in a muscle in your upper arm. You will need one dose.

Follow instructions from the healthcare staff. Tell the staff if you have ever had a severe allergic reaction to food or medicine, or carry an epinephrine autoinjector. Tell them if you feel any reaction after you have the shot. You may be asked to stay for some time after getting the vaccine so you can be monitored.

Side effects: What to report

The vaccine will have side effects for some people. A vaccine activates a person’s immune system. It causes the immune system to create antibodies and immune cells to fight off a specific virus or bacteria. When your immune system goes into action, you may feel your immune system kick into gear as though it’s fighting an illness. This does not mean you are infected with an illness. It means that your immune system is working.

People in the COVID-19 vaccine trials for this vaccine commonly had soreness where the shot was given, tiredness, headaches, muscle aches, and nausea for a day or two. Fewer people had redness and swelling at the injection site. These are all signs that your immune system is working on its defense. You can get these kinds of effects after many kinds of vaccines. But these symptoms should last a short time. In comparison, COVID-19 symptoms can be severe and last much longer, and cause complications, long-term illness, and death. The FDA approval process makes sure that the discomfort and risks of a vaccine outweigh the risks and complications of the illness it helps prevent.

Very rare cases of blood clots and low blood platelets have been reported about 1 to 2 weeks after getting the J&J vaccine. For this reason, the FDA generally advises the mRNA vaccine (Moderna or Pfizer) over the J&J vaccine. The FDA still advises the J&J vaccine if the mRNA vaccine is not available, if the person has a risk of serious side effects from the mRNA vaccines, or if a person could not get vaccinated unless they get the J&J vaccine. It's important to remember that blood clots from the J&J vaccine are very rare--about 4 cases per 1 million people. The risk of complications from having COVID-19 are greater that the risks from the vaccine. Talk with your healthcare provider.

Allergic reactions

In general, the COVID-19 vaccines are very safe. They have been tested on thousands of people and given to millions of people. Non-severe allergic reactions have happened in a few people up to 4 hours after getting the vaccine. The vaccine clinic may ask you to stay on-site for a period of time after you get the vaccine. This is to make sure you don't have an immediate reaction, and to treat you if you have one.

Talk with your healthcare provider before you get a COVID-19 vaccine. Tell them if you have ever had an immediate reaction to any vaccine, even if the reaction was not severe. Your provider will help you weigh the risks and benefits of the COVID-19 vaccine for you.

The CDC has a smartphone app called V-Safe to help you report side effects. To access this app, see "To learn more" below.

Severe allergic symptoms

Severe allergic reactions are rare. If you get a COVID-19 vaccine and think you may be having a severe allergic reaction after leaving the vaccine clinic, call 911. Severe symptoms include:

• Trouble breathing

• Wheezing

• Trouble swallowing or feeling like your throat is closing

• Cool, moist, pale, or blue-tinted skin

• Hoarse voice or trouble speaking

• Chest pain

• Fainting

• Swelling in the eyes, mouth, face, or tongue

• Seizure

• Feeling very drowsy or having trouble awakening

• Fast heart rate

• Nausea, vomiting, diarrhea, stomach cramps, or abdominal pain

After you get the COVID-19 vaccine

When you get any COVID-19 vaccine:

• It’s still possible to get COVID-19. Like most vaccines, the COVID-19 vaccines are not 100% effective at preventing the disease, especially with several strains (variants) of COVID-19 like delta and omicron. But the vaccine works well to keep you from getting seriously ill if you get the virus. You should still take care to prevent contact with sick people and follow local advice about staying safe.

• You should still follow instructions for masks and social distancing. Follow your local, state, and national instructions about wearing a mask. Follow guidelines about social distancing and staying away from crowds.

Talking with your healthcare provider

You may have a lot of questions about the vaccine for yourself. Should you get it? If so, when? What about a booster? What are the risks and benefits to you? The best way to answer these questions is to talk with your healthcare provider. They can let you know when and what kind of vaccine is available, and what you should consider.

To learn more

• CDC: COVID-19 Vaccines

• FDA: COVID-19 Vaccines

• V-Safe After Vaccination Health Checker

Last modified date: 3/31/2023