Two vaccines have currently received FDA emergency-use authorization and are available in the U.S.: the Pfizer-BioNTech COVID-19 Vaccine and the Moderna COVID-19 Vaccine.

These two vaccines are similar in important ways:

  • Rigorous testing. Both vaccines have been through a rigorous testing and review process nationally and additionally by the Western States Scientific Safety Review Workgroup, and the State of California.
  • Highly effective. Current research shows both vaccines provide 94-95% effectiveness at preventing COVID-19 infection.
  • Common mild side effects. People have experienced common mild side effects from both vaccines, such as pain at the site of the injection and headache or chills for a few days after getting the vaccine.
  • mRNA vaccines. Both are mRNA vaccines that provide an instruction manual for your immune system to develop antibodies that will fight the virus that causes COVID-19.  They do not affect or interact with our DNA in any way.
  • No live virus. Neither vaccine contains the SARS-CoV-2 virus. The vaccines cannot give you COVID-19.
  • Two doses. Both vaccines are administered in two doses, several weeks apart.

The vaccines are also different in some ways:

  • Age when you can get the vaccine. The Pfizer-BioNTech vaccine has received FDA emergency-use authorization to prevent COVID-19 in people 16 years old and older, while the Moderna vaccine has received such authorization for those 18 years and older.
  • Timing of second dose. The second dose of the Pfizer-BioNTech vaccine is available after 21 days, while the second dose of the Moderna vaccine is available after 28 days.

Due to the limited and quickly-changing supply of vaccines and the complexity involved in distributing it, we are not able to provide an option to choose which of these two authorized vaccines you will to receive at a County vaccine site. 

To learn more about the lot of Moderna vaccine that has been paused statewide, read our recent news release. 


For more information on the Moderna COVID-19 Vaccine, visit:
For more information on the Pfizer-BioNTech COVID-19 Vaccine, visit:
What to expect after getting a vaccine