COVID-19 vaccine boosters and third doses

Updated May 11, 2022

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:

The CDC recommends third doses for immunocompromised people age 5 and older of an mRNA vaccine from Pfizer or Moderna. (Pfizer remains the only vaccine approved for ages 5-17.) The third dose must be given at least four weeks after the second dose. Some of the conditions and treatments that result in immunosuppression include, but are not limited to, the following:

  • Active treatment for solid tumor and hematologic malignancies
  • Receipt of solid-organ transplant and taking immunosuppressive therapy
  • Receipt of chimeric antigen receptor (CAR)-T-cell or hematopoietic stem cell transplant (within 2 years of transplantation or taking immunosuppression therapy)
  • Moderate or severe primary immunodeficiency (e.g., DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Advanced or untreated HIV infection
  • Active treatment with high-dose corticosteroids (i.e., ≥20 mg prednisone or equivalent per day when administered for ≥2 weeks), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor-necrosis factor (TNF) blockers, and other biologic agents that are immunosuppressive or immunomodulatory.

A booster (fourth) dose is also recommended for those who are immunocompromised. This dose would be given 3 months after the additional primary shot (or third dose). For those who received Johnson & Johnson, the CDC recommends a booster (third) dose of an mRNA vaccine (Pfizer or Moderna) 2 months after the initial two doses.

The CDC recommends a Pfizer booster dose at least 5 months after the initial two doses for anyone 12 years and older.

Moderna boosters are available for ages 18 and older at least 5 months after the second dose.

Anyone who received a single dose Johnson & Johnson vaccine is eligible for a COVID-19 booster at least 2 months after their first dose.

Schedule your COVID-19 boosters or third dose through MyUCDavisHealth or on California's MyTurn.ca.gov.

View the CDC chart of who is eligible for a COVID-19 booster

The FDA and CDC authorized a second booster dose of either Pfizer or Moderna COVID-19 vaccines for the following groups:

  • People ages 50 and older: The second booster is to be given at least 4 months after the first booster dose.
  • People ages 12 and older who are immunocompromised: The second booster is to be given at least 4 months after the first booster dose. Pfizer remains the only approved vaccine for ages 12-17.

UC Davis Health is offering appointments for this additional COVID-19 booster dose. Schedule your appointment on MyUCDavisHealth.

People with compromised immune systems ages 5 and older: The CDC recommends that “people with moderately to severely compromised immune systems receive an additional dose of mRNA COVID-19 vaccine at least 28 days after a second dose” of Pfizer or Moderna COVID-19 vaccine. Pfizer remains the only vaccine approved for ages 5-17. For those who received an initial dose of Johnson & Johnson, it's recommended that they get a second mRNA vaccine dose (Pfizer or Moderna) 4 weeks after the first dose. This group can also get a booster (third or fourth) dose of an mRNA vaccine.

People ages 12 and older who received Pfizer: The CDC recommends a Pfizer booster dose at least 5 months after the initial two doses.

People ages 18 and older who received Moderna: The CDC recommends a Moderna booster dose at least 5 months after the initial two doses.

People who received a single dose Johnson & Johnson vaccine: Anyone 18 years and older who got a Johnson & Johnson shot is eligible for a COVID-19 booster dose at least two months after their first dose.

For patients with previous COVID-19 infections, the CDC has advised that more time between infection and vaccination may improve immune response. You may want to consider a 3-month interval before your first or second booster doses or discuss the timing of your booster with your physician. 

For patients with previous COVID-19 infections, the CDC has advised that more time between infection and vaccination may improve immune response. You may want to consider a 3-month interval before your first or second booster doses or discuss the timing of your booster with your physician. 

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 MyTurn.ca.gov 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.

UC Davis Health employees who received two doses of the Pfizer or Moderna COVID-19 vaccine more than five months ago are eligible for a booster shot. Additionally, employees who received a Johnson & Johnson vaccine can also get a booster shot two months after their initial dose. Employee Health Services is also offering flu vaccines for employees.

The UC Office of the President updated its COVID-19 vaccination policy to require all UC health care workers get a COVID-19 booster by Jan. 31.

Related: UC Office of the President announces that all UC employees must receive a COVID-19 booster

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.

On Oct. 21, the CDC updated its recommendations to allow for the mixing of COVID-19 vaccine boosters from different manufacturers. In other words, if you received your first two doses of Pfizer, the CDC’s recommendations allow for you to get a booster dose of the Moderna vaccine – or vice-versa.

UC Davis Health plans to match previous vaccine doses with the booster shot.

Experts don’t know yet how often additional COVID-19 vaccine doses will be needed. Data is needed to see how protection varies by specific vaccine and in different populations. This is likely to evolve as the pandemic evolves and may be impacted by the development of new variants.

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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