When a vaccine is found to meet safety and effectiveness standards by the FDA, the Advisory Committee on Immunization Practices (ACIP) will review the data before making vaccine use recommendations to CDC. The vaccines can then be made available for use in the U.S. by approval or emergency used authorization.
With most COVID-19 vaccines, you will need two shots a few weeks apart for them to work. It will take a week or two after the second shot for your body to build protection.
Vaccine Safety Monitoring
After a vaccine is authorized or approved for use, many vaccine safety monitoring systems watch for adverse events (possible side effects). This monitoring is critical to help ensure that the benefits continue to outweigh the risks for people who receive vaccines. CDC will link with existing monitoring systems to new safety surveillance systems:
Expected and temporary vaccine side effects
COVID-19 vaccination will help protect you from getting COVID-19, but you may have some side effects:
The common and temporary side effects that are expected after a COVID-19 vaccination may affect your ability to do some activities, but should go away in a few days – such as arm pain, red swelling at injection site, fever, chills, tiredness, and headache. However, these mild side effects can be lessened by taking over-the-counter medicine such as ibuprofen or acetaminophen. It also helps to drink plenty of fluids, exercise your arm, and apply a clean, damp washcloth over the area. After 24 hours, if the redness/tenderness increases or after a few days the side effects are not going away, call your healthcare provider. Remember to get the second shot even if you have side effects after the first shot, unless a vaccination provider or your doctor tells you not to get a second shot.
Possible allergic reaction
Some people may have severe allergic reactions to an ingredient in vaccines. CDC has learned of reports that some people have experienced severe allergic reactions (anaphylaxis) after getting a COVID-19 vaccine.
CDC recommends that everyone who receives the COVID-19 vaccines should be monitored onsite for an additional 15 minutes for severe allergic reaction. Those with a history of severe allergic reactions should be monitored for 30 minutes. If you get a COVID-19 vaccine and you think you might be having a severe allergic reaction after leaving the vaccination site, seek immediate medical care by calling 9-1-1.