About COVID-19 Vaccines

The Centers for Disease Control and Prevention (CDC) has developed a list of top questions and things to know about the vaccine. Below is an abbreviated version; please visit CDC’s “8 things to know” for full details.

1. The safety of COVID-19 vaccines is a top priority.
2. COVID-19 vaccination will help protect you from getting COVID-19. Two doses are needed for the Pfizer-BioNTech and Moderna vaccines. One dose is needed for the Johnson & Johnson vaccine.
3. CDC is making recommendations for who should be offered COVID-19 vaccine first when supplies are limited.
4. There is currently a limited supply of COVID-19 vaccine in the U.S., but supply will increase in the weeks and months to come.
5. After COVID-19 vaccination, many people experience some side effects. This is a normal sign that the body is building protection.
6. Cost is not an obstacle to getting vaccinated against COVID-19.
7. The first COVID-19 vaccines are being used under Emergency Use Authorizations from the U.S. Food and Drug Administration (FDA). Many other vaccines are still being developed and tested.
8. COVID-19 vaccines are one of many important tools to help us stop this pandemic.

The Pfizer-BioNTech and Moderna vaccines are similar in how they work. Both vaccines consist of genetic material called mRNA encased in tiny particles that deliver the mRNA into our cells. From there, our cells translate the mRNA to a protein, which stimulates the immune system to make antibodies that protect against the virus. These vaccines do not have any impact on our own genetic material, and the mRNA material breaks down in the body shortly after it is taken into our cells. Both vaccines require two doses to be fully effective.

The Johnson & Johnson vaccine is a viral vector vaccine, meaning it uses a modified form of a different virus to deliver material into human cells and start the immune response process. This particular vaccine uses a modified adenovirus to deliver small segments of DNA from the virus that causes COVID-19. The adenovirus can enter cells but it can’t replicate or cause illness. Human cells take up the COVID-19 DNA fragments and transcribe them into mRNA, and the process proceeds as described above for mRNA vaccines to create an immune response that prepares the body to fight off COVID-19. Unlike the Pfizer-BioNTech and Moderna vaccines, only one dose is required for protection with the Johnson & Johnson vaccine.

Importantly, the COVID-19 vaccines do not contain the virus that causes COVID-19. It is NOT possible to contract COVID-19 from any of the vaccines currently approved for use in the US.

CDC: Understanding mRNA COVID-19 vaccines

CDC: Understanding Viral Vector COVID-19 Vaccines

The FDA is monitoring the safety of authorized COVID-19 vaccines through both passive and active safety surveillance systems. All data on the Moderna and Pfizer vaccines that are currently available indicate that the vaccines are safe and that adverse reactions are very rare. Some individuals do experience minor side effects that reflect the body’s immune response beginning; a tiny number of individuals have experienced allergic reactions and have required immediate treatment, which has been successful.

Before authorization, clinical trials were completed across the globe with tens of thousands of participants in each trial. The FDA used the data from these trials to evaluate the vaccines’ safety and efficacy to make the emergency use determinations. The vaccines will continue to be studied — under CDC surveillance and by other means — to learn about longer-term safety and effectiveness. Since these vaccines were first approved for use, tens of millions individuals around the world have been immunized, further supporting their safety.

In April 2021, distribution of the Johnson & Johnson vaccine was temporarily paused while the FDA and the CDC investigated a few reported cases in which recipients experienced a rare form of blood clots. Following a review of all available data, the CDC and FDA lifted the recommended pause on the J&J vaccine, stating that the vaccine's benefits far outweigh its risks. Women younger than 50 years old should be aware of the rare but increased risk of this adverse event for that age group; there are other COVID-19 vaccine options available for which this risk has not been seen. The safety of all COVID-19 vaccines is monitored by local, state, and federal officials and agencies.

CDC: Ensuring the safety of COVID-19 vaccines in the U.S.

All vaccines currently available in the U.S. have met rigorous scientific safety standards. Because each of the vaccines were studied in different times and locations, and in populations with differing background incidence of disease and circulation of virus variants of concern, it is not possible to compare them against each other.

CDC: Information about the Pfizer-BioNTech vaccine
CDC: Information about the Moderna vaccine
CDC: Information About Johnson & Johnson/Janssen vaccine
CDC: Ensuring COVID-19 vaccines work

Scientific studies suggest that two doses for the Pfizer-BioNTech and Moderna vaccines are optimal for achieving immunity. For the Pfizer-BioNTech vaccine, the second dose is administered 21 days after the first dose; for the Moderna vaccine, 28 days after the first dose.

The second dose must be the same type as the first one received. At the time of the first vaccination, most centers schedule individuals for their second dose. The second dose should be administered as close to the recommended interval as possible.

The Johnson & Johnson vaccine is effective after only one dose.

No. The vaccines do not contain live or deactivated/dead COVID-19 virus material, so they cannot give anyone COVID-19. If after receiving the vaccine an individual experiences symptoms that last more than a couple of days, like a fever, particularly if it is accompanied by cough, a regular health care provider should be contacted. Individuals who are diagnosed with the virus after vaccination are thought to have been exposed to the virus prior to getting the vaccine, or before it induced immunity. In this case, testing will be important to determine current COVID-19 status, and any need for isolation or quarantine. It is possible, of course, symptoms may reflect another infection such as a cold or the flu, something that can be determined by a health care provider.

Soreness, redness and swelling at the injection site are the most common reactions, and are typically seen with many types of vaccines. In addition, fever, muscle aches and headaches can develop in a percentage of patients after the COVID-19 vaccine. Medical professionals have advised that such reactions do not reflect an allergy to the vaccine but are usually signs that the body is creating the immunity needed from the vaccine. Medical professionals advise that symptoms typically go away on their own within a couple of days and can be relieved with non-prescription medications (e.g., ibuprofen or acetaminophen) but individuals who have been vaccinated should contact their own health care provider with any concerns, or if any of these symptoms are very severe or if they persist.

CDC: What to expect after getting a COVID-19 vaccine

FDA: Fact sheet for recipients of Johnson & Johnson COVID-19 vaccine

Yes. Due to the severe health risks associated with COVID-19 and the fact that re-infection with COVID-19 is possible, the CDC has recommended that COVID-19 vaccine be offered regardless of a prior COVID-19 infection. At this time, experts do not know how long someone is protected from getting sick again after recovering from COVID-19. The immunity someone gains from having an infection, called natural immunity, varies from person to person. How long natural immunity typically lasts is still an area under investigation.

CDC: Benefits of getting a COVID-19 vaccine

This is still under investigation by vaccine experts and researchers who don’t yet know what antibody levels are needed to protect against reinfection. Therefore, health experts recommend individuals receive the vaccine even if they have already had COVID; however, it is not recommended to take the vaccine during the period of COVID-19 illness itself. A person who has tested positive for COVID-19 and is currently completing isolation, must wait for at least 10 days after the positive test and upon release from isolation to obtain the vaccine.

CDC: Facts about COVID-19 vaccines

The duration of protection from the vaccine against COVID-19 is not yet known. Additional evaluation of the vaccines are in process to learn how often vaccination must be repeated, if ever, to provide protection.

Health officials are studying the effectiveness of the currently available vaccines against variants of the coronavirus. So far, studies suggest that antibodies generated through vaccination with currently authorized vaccines recognize the most widespread virus variants.

Stopping a pandemic requires using all the tools available, and it is important for us all to be using as many of these tools as possible as to protect ourselves and our community. Vaccines work with the immune system so the body will be ready to fight the virus and reduce or eliminate illness if a person has been exposed. Other preventative measures, like covering the mouth and nose with a mask and staying at least six feet away from others, help reduce the chance of being exposed to the virus or spreading it. Together, the vaccine and following public health guidance will offer the best protection.

CDC: Benefits of getting a COVID-19 vaccine

Yes. While experts learn more about the protection that COVID-19 vaccines provide under real-life conditions, it is important for everyone to continue using all the tools available to help stop this pandemic (e.g., wearing face coverings, practicing physical distancing, frequent hand washing, avoiding large groups and unnecessary travel).

There is not enough information currently available to say if or when the CDC will stop recommending that people wear masks and avoid close contact with others to help prevent the spread of the virus that causes COVID-19. Experts need to understand more about the protection that COVID-19 vaccines provide before making that decision. Other factors, including how many people get vaccinated and how the virus is spreading in communities, will also affect this decision.

CDC: How to protect yourself and others

Before receiving the vaccine, all individuals will be asked by the healthcare professional administering the vaccine if they have a fever, have an allergy, are immunocompromised or are on a medicine that affects the immune system.

Recommendations from the CDC include:

• Health experts recommend individuals receive the vaccine even if they have already had COVID; however, it is not recommended to take the vaccine during the period of COVID-19 illness itself. Individuals who tested positive for COVID-19 and are currently completing isolation must wait for at least 10 days after the positive test and upon release from isolation to obtain the vaccine.
• While people who are immunocompromised will be offered the vaccine, we do not yet know how well it works.
• Anyone recently vaccinated against another illness, such as the flu, should wait 14 days before taking this vaccine.
• The vaccine is not available to children under 16 at this time, though Pfizer is currently testing it in children as young as 12, and other studies will include even younger children.
• It is not recommended that anyone receive the vaccine who is allergic to any of the vaccine's ingredients. Until we have more information, those with a history of a severe allergic reaction, including anaphylaxis, to any vaccine or injectable medicine are being advised by medical professionals to be cautious about getting the vaccine. Any person to whom this might apply should discuss with their provider to decide how to proceed.
• For individuals who are pregnant, the American College of Obstetricians and Gynecologists recommends that the vaccine still be given, and that a conversation with their health care provider prior to vaccination is not required but may be helpful in guiding decision making.

CDC: Information about the Pfizer-BioNTech vaccine
CDC: Information about the Moderna vaccine

No. The coronavirus that causes COVID-19 and the influenza virus are completely different viruses, and their vaccines are also different. The flu vaccine does not protect a person from becoming infected with COVID-19, so it is important to get both vaccines to ensure protection from both viruses, especially going into the winter months. Recent studies have shown that individuals who have received a flu vaccine have a lower risk of being hospitalized if they get COVID-19.