COVID-19 (coronavirus) vaccine: Get the facts

Vaccines to prevent coronavirus disease 2019 (COVID-19) are perhaps the best hope for ending the pandemic. But as the U.S. Food and Drug Administration (FDA) continues approving or authorizing emergency use of COVID-19 vaccines, you likely have questions. Find out about the benefits of the COVID-19 vaccines, how they work, the possible side effects and the importance of continuing to take infection prevention steps.

A COVID-19 vaccine might:

• Prevent you from getting COVID-19 or from becoming seriously ill or dying due to COVID-19
• Prevent you from spreading the virus that causes COVID-19 to others
• Add to the number of people in the community who are protected from getting COVID-19 — making it harder for the disease to spread and contributing to herd immunity
• Prevent the virus that causes COVID-19 from spreading and replicating, which allows it to mutate and possibly become more resistant to vaccines

Currently, several COVID-19 vaccines are in clinical trials. The FDA continues to review the results of these trials before approving or authorizing COVID-19 vaccines for use. But because there is an urgent need for COVID-19 vaccines and the FDA's vaccine approval process can take months to years, the FDA first gave emergency use authorization to COVID-19 vaccines based on less data than is normally required. The data must show that the vaccines are safe and effective before the FDA can give emergency use authorization or approval. Vaccines with FDA emergency use authorization or approval include:

• Pfizer-BioNTech COVID-19 vaccine. The FDA has approved the Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, to prevent COVID-19 in people age 16 and older. The FDA approved Comirnaty after data found the vaccine is safe and effective. The Pfizer-BioNTech COVID-19 vaccine is 91% effective in preventing the COVID-19 virus with symptoms in people age 16 and older.

  The vaccine is still under an emergency use authorization for children ages 12 through 15. The vaccine is 100% effective in preventing COVID-19 in children ages 12 through 15. It requires two injections given 21 days apart. The second dose can be given up to six weeks after the first dose, if needed.

  The vaccine is now also available under an emergency use authorization for children ages 5 through 11. This vaccine is about 91% effective in preventing COVID-19 in children ages 5 through 11. It requires two injection, given 21 days apart. It also contains a lower dose than the Pfizer-BioNTech COVID-19 vaccine used for people age 12 and older.

• Moderna COVID-19 vaccine. The Moderna COVID-19 vaccine is 94% effective in preventing COVID-19 with symptoms. This vaccine is authorized for people age 18 and older. It requires two injections given 28 days apart. The second dose can be given up to six weeks after the first dose, if needed.
• Janssen/Johnson & Johnson COVID-19 vaccine. In clinical trials, this vaccine was 66% effective in preventing the COVID-19 virus with symptoms — as of 14 days after vaccination. The vaccine also was 85% effective at preventing severe disease with COVID-19 — at least 28 days after vaccination. This vaccine is authorized for people age 18 and older. It requires one injection. The FDA and the Centers for Disease Control and Prevention (CDC) have recommended that use of this vaccine continue in the U.S. because the benefits outweigh the risks. If you are given this vaccine, you should be educated about the possible risks and symptoms of a blood clotting problem.

The CDC recommends getting an mRNA COVID-19 vaccine over getting the Janssen/Johnson & Johnson COVID-19 vaccine. But getting any COVID-19 vaccine is better than not getting a COVID-19 vaccine.

Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use messenger RNA (mRNA). Coronaviruses have a spikelike structure on their surface called an S protein. COVID-19 mRNA vaccines give cells instructions for how to make a harmless piece of an S protein. After vaccination, your cells begin making the protein pieces and displaying them on cell surfaces. Your immune system will recognize the protein and begin building an immune response and making antibodies.

The Janssen/Johnson & Johnson COVID-19 vaccine is a vector vaccine. In this type of vaccine, material from the COVID-19 virus is inserted into a different kind of weakened live virus, such as an adenovirus. When the weakened virus (viral vector) gets into your cells, it delivers material from the COVID-19 virus that gives your cells instructions to make copies of the S protein. Once your cells display the S proteins on their surfaces, your immune system responds by creating antibodies and defensive white blood cells. If you become infected with the virus that causes COVID-19, the antibodies will fight the virus.

Viral vector vaccines can't cause you to become infected with the COVID-19 virus or the viral vector virus. Also, the material that's delivered doesn't become part of your DNA.

No. The COVID-19 vaccines currently being developed in the U.S. don't use the live virus that causes COVID-19. As a result, the COVID-19 vaccines can't cause you to become sick with COVID-19 or shed any vaccine components.

Keep in mind that it will take a few weeks for your body to build immunity after getting a COVID-19 vaccination. As a result, it's possible that you could become infected with the virus that causes COVID-19 just before or after being vaccinated.

A COVID-19 vaccine can cause mild side effects after the first or second dose, including:

• Pain, redness or swelling where the shot was given
• Fever
• Fatigue
• Headache
• Muscle pain
• Chills
• Joint pain
• Nausea and vomiting
• Feeling unwell
• Swollen lymph nodes

You'll be monitored for 15 minutes after getting a COVID-19 vaccine to see if you have an allergic reaction. Most side effects go away in a few days. Side effects after the second dose might be more intense. Many people have no side effects.

A COVID-19 vaccine may cause side effects similar to signs and symptoms of COVID-19. If you've been exposed to COVID-19 and you develop symptoms more than three days after getting vaccinated or the symptoms last more than two days, self-isolate and get tested.

It's recommended that you get a COVID-19 vaccine if you are trying to get pregnant or might become pregnant in the future. There is no evidence that any COVID-19 vaccines cause fertility problems.

A small number of women have reported experiencing temporary menstrual changes after getting a COVID-19 vaccine. A small study has also shown that some women experienced temporary menstrual changes after getting COVID-19. It's not clear if getting COVID-19 or a COVID-19 vaccine causes these changes. Further research is needed.

Keep in mind that many things can affect menstrual cycles, including infections, stress, sleep problems and changes in diet or exercise.

If you become pregnant after getting the first dose of a COVID-19 vaccine that requires two doses, it’s recommended that you get your second shot.