COVID-19 vaccine boosters and third doses

Updated Jan. 19, 2023

COVID-19 vaccine boosters and third doses are available for certain people. You can schedule your booster or third dose with UC Davis Health. Here's what you need to know from our UC Davis Health experts:

In the fall of 2022, the U.S. Food and Drug Administration (FDA) and the U.S. Centers for Disease Control and Prevention (CDC) approved an "updated booster" known as the bivalent vaccine for ages 5 and older. In December 2022, the bivalent booster from Moderna was approved under emergency use for patients 6 months and older, while a third dose (not a booster) of Pfizer's bivalent formulation was approved for ages 6 months to 4 years. The CDC's recommendation is for everyone in this age range to get a bivalent booster, even if you've received one or more of the original boosters.

If you're unsure when to get your booster and which booster you're eligible for, the CDC has a tool to help you decide. The tool prompts you to answer questions about your age range, when you've last received a vaccine or booster, and a few other pieces of information about your vaccine status. 

Find out when you're eligible for a COVID-19 booster 

Schedule your COVID-19 booster or any dose on MyUCDavisHealth

Learn more about bivalent boosters from the California Department of Public Health

Bivalent vaccines, which are being called the "updated boosters," contain two mRNA components of the COVID-19 virus. It includes the original SARS-CoV-2 strain and another strain that is common between the omicron BA.4 and BA.5 viruses.

Both Moderna and Pfizer-BioNTech have bivalent single-dose boosters that have been authorized by the FDA and CDC.

UC Davis Health is offering bivalent boosters for anyone at any of our COVID-19 vaccine clinic locations. You can schedule your bivalent vaccine through MyUCDavisHealth (non-patients without a login will have to create an account) or by calling 916-703-5555. (In MyUCDavisHealth, click on Visits > Schedule Appointment > COVID Vaccination. You will then be prompted to answer which vaccines you have received already.)

Learn more about bivalent vaccines from the U.S. Food and Drug Administration (FDA)

View the California Department of Public Health's statement on bivalent vaccines

The CDC recommends immunocompromised people ages 6 months and older receive an additional primary series dose of Moderna or ages 5 years and older receive an additional primary series dose of Pfizer. The additional dose must be given at least four weeks after the second dose of Pfizer or Moderna or at least four weeks after one dose of Johnson & Johnson. Some of the conditions and treatments that result in immunosuppression include, but are not limited to, the following:

  • Active cancer treatment for tumors or blood cancers
  • Organ transplant and is taking immunosuppressants
  • Received CAR-T therapy or a stem cell transplant within the last 2 years
  • Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Advanced or untreated HIV infection
  • Taking immunosuppressants (such as high-dose corticosteroids)
  • Dialysis

Schedule your COVID-19 boosters or third dose through MyUCDavisHealth or on California's

View the CDC's breakdown of boosters for immunocompromised people

If you've had a recent COVID-19 infection, the CDC recommends that you consider delaying your booster dose by 3 months after symptoms first appear or a positive test.

If you are eligible for a COVID-19 vaccine booster or third dose, UC Davis Health patients and non-patients can schedule an appointment at MyUCDavisHealth. You can also use California's vaccine scheduling portal.

Here are instructions to schedule your COVID-19 booster vaccination with one of our UC Davis Health locations:

  • Log into your MyUCDavisHealth account (on desktop or mobile)
  • Click "Visits" at the top
  • Click "Schedule an Appointment"
  • Scroll down and click COVID Vaccination (at the bottom on mobile or on the bottom right for desktop users)
  • Fill in the questionnaire, which will best guide you to the appropriate scheduling options.

Anyone who received a single dose Johnson & Johnson vaccine is eligible to received a booster shot or second dose of an mRNA vaccine (Pfizer or Moderna), according to the CDC’s criteria. To schedule a booster or second dose with UC Davis Health, please call 916-703-5555 Monday-Friday 8 a.m.-5 p.m.

Protection against infection decreases over time. As a result, about 5 months after the initial COVID-19 vaccine, fully vaccinated people have more risk for breakthrough infections.

For people younger than 65 years of age and who don’t have underlying conditions that increase their risk of getting the virus, COVID-19 breakthrough infections are generally mild. Most of the time, these infections don't cause severe disease or hospitalization. Therefore, this group may choose a booster vaccine to decreased risk of breakthrough infection.

People 65 and older or those with underlying conditions are at higher risk for severe infection. A COVID-19 booster dose is recommended for these groups

For immunocompromised patients, the immune response to the first two doses of mRNA vaccine may not result in enough protection, so a third COVID-19 vaccine is recommended.

Side effects following a booster or third dose of COVID-19 vaccine are similar to side effects following the second dose, with slightly more pain at the injection site, fever, chills, and fatigue. No serious side effects were found in third dose studies.

It was understood that COVID-19 vaccines would not protect people forever. Although some vaccine manufacturers have publicly stated that they believe boosters are needed due to declining protection, there is very little data at this time that shows decreasing protection. So far, protection appears to be durable.

According to CDC data, the Moderna vaccine is 94.1% effective at preventing laboratory-confirmed COVID-19 infection in people who received two doses and had no evidence of being previously infected.

While the vaccines' effectiveness at preventing symptoms and illness declines over time as the body processes its immune response, all of the vaccines are still highly effective against hospitalization and death. These third doses of vaccine are aimed largely at preventing illness and reducing spread during the shorter time a vaccinated person may be ill. However, the initial two-dose series is still highly effective at preventing serious infections leading to hospitalization or death.

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