The main types of COVID-19 vaccines currently available in the U.S. or being studied include:

• Messenger RNA (mRNA) vaccine. This type of vaccine gives your cells instructions for how to make the S protein found on the surface of the COVID-19 virus. After vaccination, your muscle cells begin making the S protein pieces and displaying them on cell surfaces. This causes your body to create antibodies. If you later become infected with the COVID-19 virus, these antibodies will fight the virus.

  Once the protein pieces are made, the cells break down the instructions and get rid of them. The mRNA in the vaccine doesn’t enter the nucleus of the cell, where DNA is kept. Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use mRNA.

• Vector vaccine. In this type of vaccine, material from the COVID-19 virus is placed in a modified version of a different virus (viral vector). The viral vector gives your cells instructions to make copies of the COVID-19 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 later become infected with the COVID-19 virus, 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. The Janssen/Johnson & Johnson COVID-19 vaccine is a vector vaccine. AstraZeneca and the University of Oxford also have a vector COVID-19 vaccine.

• Protein subunit vaccine. Subunit vaccines include only the parts of a virus that best stimulate your immune system. This type of COVID-19 vaccine contains harmless S proteins. Once your immune system recognizes the S proteins, it creates antibodies and defensive white blood cells. If you later become infected with the COVID-19 virus, the antibodies will fight the virus.

  The Novavax COVID-19 vaccine is a protein subunit vaccine.

The COVID-19 vaccines available in the United States are:

• 2023-2024 Pfizer-BioNTech COVID-19 vaccine, available for people age 6 months and older.
• 2023-2024 Moderna COVID-19 vaccine, available for people age 6 months and older.
• 2023-2024 Novavax COVID-19 vaccine, available for people age 12 years and older.