COVID-19 Vaccines

Page last updated on 5/16/2024

Latest Updates

The updated COVID-19 vaccine is available throughout San Diego County. 


Vaccines authorized by the U.S. Food and Drug Administration (FDA) currently include:

These vaccines are given as a shot in the muscle of the upper arm or in the thigh of a young child. COVID-19 vaccine ingredients are considered safe for most people.

How do the COVID-19 vaccines work? 

  • The vaccines teach your body to recognize COVID-19, so it is prepared to fight the virus.
  • Messenger RNA vaccines (mRNA), like Pfizer-BioNTech and Moderna, provide instructions for your body to build a small protein that looks like a piece of COVID-19. This protein helps your body recognize the virus if you become infected. 
  • Protein subunit vaccines, such as Novavax, include harmless proteins of the virus that cause COVID-19. This helps your body recognize the virus if you become infected.
  • Bivalent vaccines ("updated vaccine") protects against both the original virus that causes COVID-19 and the Omicron variant BA.4 and BA.5.

How well do COVID-19 vaccines work?

  • People who are up-to-date have lower risk of severe illness, hospitalization, and death from COVID-19 than people who are unvaccinated or who have only received the primary series.
  • Updated COVID-19 boosters can help build up protection that has decreased since previous vaccination. The updated boosters provide added protection against the recent Omicron subvariants that are more contagious than the previous ones. The recent subvariants, BA.4 and BA.5, are very closely related to the original variant, Omicron, with very small differences between itself and the original variant.

Are COVID-19 vaccines safe?

  • COVID-19 vaccines have undergone – and will continue to undergo – the most intensive safety monitoring in U.S. history. 
  • Evidence from the hundreds of millions of COVID-19 vaccines already administered in the U.S., and the billions of vaccines administered globally, demonstrates that they are safe and effective.

Are there side effects to the COVID-19 vaccine?

  • There may be some mild side effects that go away in a day or two. Side effects are a sign that the vaccine is working. Side effects could include:
    • Pain, redness, or swelling in the arm where you received the vaccine. You can apply a cool, wet washcloth to reduce pain.
    • Mild flu-like symptoms, like tiredness, nausea, muscle aches, chills, headache, or fever. Drink plenty of fluids and rest to feel more comfortable.
  • Severe allergic reactions to vaccines are rare but can happen. 

What are booster doses?

  • A booster dose refers to a vaccine given after the primary series to boost protection which might have waned over time.

What is the difference between monovalent and bivalent boosters?

  • Previous boosters are called “monovalent” because they were designed to protect against the original (i.e., one) virus that causes COVID-19. 
  • Updated boosters are called “bivalent” because they protect against both (i.e., two viruses) the original virus and the Omicron variants that causes COVID-19. More recent variants of Omicron are also covered by the vaccine.