The U.S. Food and Drug Administration (FDA) issued emergency use authorizations (EUAs) for vaccines to prevent coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in individuals 16 years of age and older:
- Pfizer-BioNTech COVID-19 vaccine
- Moderna COVID-19 vaccine
- Janssen (Johnson & Johnson) COVID-19 vaccine
All currently available vaccines have been found to be safe, effective, and reduce the risk of severe illness and death from COVID-19.
In addition to the above vaccines, other large-scale (Phase 3) clinical trials in progress for COVID-19 vaccines in the U.S. include:
Vaccines help the body produce immunity to infection by imitating the infecting agent. Vaccines almost never cause serious illness, but instead boost the body’s adaptive immune function to produce T-lymphocytes and antibodies (parts of the immune system that help the body fight germs). Once the simulated infection created by the vaccine goes away, the body has a “memory” of T-lymphocytes and B-lymphocytes that remember how to fight that infection in the future.
After the COVID-19 vaccine is administered and the body is building its defenses, people may experience mild side effects starting a day or two after receiving the vaccine that can last a few days. This is normal and expected and a sign the body’s immune system is responding as it should.
Common side effects and reactions to the COVID-19 vaccines include:
- Injection site reactions (pain, tenderness, redness, swelling)
- Muscle aches or pains
More people experienced these side effects after the second dose of the Pfizer-BioNTech COVID-19 vaccine and the Moderna COVID-19 vaccine than after the first dose.
Rarely, severe allergic reactions, including anaphylaxis, can occur after receiving any vaccine. This type of reaction has only occurred in about 2 to 5 people per million vaccinated in the U.S. These kinds of allergic reactions usually occur within 30 minutes after vaccination and can be immediately and effectively treated. People who are allergic to specific ingredients in the current vaccines are advised to avoid that particular vaccine. Those prone to allergic reactions, but who do not have a known allergy to a component of the vaccine, are advised to receive the vaccine in a healthcare facility and to wait 30 minutes (instead of 15) following the injection.
There is a Vaccine Adverse Event Reporting System (VAERS) in place for patients to report unexpected vaccine side effects. https://vaers.hhs.gov/
Following immunization, it can take several weeks for the body to produce the produce T-lymphocytes and B-lymphocytes needed to fight infection, so it is possible a person could become infected with COVID just before or just after vaccination because the body has not yet had time to build its defenses.
How Do the COVID-19 Vaccines Work?
Coronaviruses, including COVID-19, are named for the crown-like spikes on their surface because corona in Latin means “crown.” The current vaccines all focus on these spikes. None of the approved vaccines use the virus that causes COVID, and you cannot get COVID from the vaccines.
The Pfizer-BioNTech and Moderna mRNA vaccines use a type of technology not used in any existing vaccine. These mRNA vaccines contain a small part of the genetic code for a harmless piece of the SARS-CoV-2 spike protein (the same spike protein that is found on the surface of the virus that causes COVID-19) and it gives the body's cells instructions to make viral proteins the immune system can recognize. This allows an immune system response with the goal of preventing COVID-19 disease.
The cells then break down and get rid of the mRNA soon after they are finished using its instructions, and the mRNA does not enter the nucleus of the cells where genetic material is stored, so it does not affect a person’s DNA. The Pfizer-BioNTech and Moderna COVID-19 vaccines do not contain any live virus.
- The Pfizer-BioNTech COVID-19 vaccine requires 2 shots administered 3 weeks apart.
- The Moderna vaccine requires 2 shots administered 4 weeks apart.
The Janssen (Johnson & Johnson) vaccine uses a weakened (attenuated) virus, called an adenovirus, that causes colds in chimpanzees. The virus is genetically altered to carry a gene for a coronavirus spike protein in order to train a person’s immune system to recognize the real coronavirus and fight it.
- The Janssen (Johnson & Johnson) vaccine requires just one injection.
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