A syringe, cotton swabs and bandages at a COVID-19 vaccination station in the gymnasium of Antioch Middle School in Antioch, Calif., on May 19, 2021. (Eli Walsh/Bay City News)

Marin County’s public health department will hold a mass vaccination event Saturday for fully-vaccinated residents who are eligible for a third COVID-19 vaccine dose as a result of having a weakened immune system.

The one-day event, from the Marin Health and Human Services, will be held at the Marin Center, 20 Avenue of the Flags, San Rafael. Vaccine seekers are encouraged to make an appointment and must bring a valid identification card, their COVID-19 vaccination card and a health insurance or medical coverage card if they have one.

Vaccinations will be available to people who received their second Pfizer or Moderna vaccine dose more than 28 days ago and have received cancer treatment, received an organ or stem cell transplant, are HIV-infected or are being actively treated with high-dose corticosteroids or other immunosuppressant drugs.

“A third dose helps boost the protection for people with severely weakened immune systems,” said Dr. Matt Willis, a county public health officer. “It’s also important to remember that those of us who are fully vaccinated and have normal immune response are well protected, and don’t need an additional dose yet.”

State and federal health officials have given their approval over the last week of third doses for immunocompromised people, who are more likely to suffer so-called breakthrough COVID-19 infections because their immune response is not as robust as that of people with fully functional immune systems.

Residents who are eligible for a third vaccine dose but cannot attend the mass-vaccination event on Saturday are encouraged to contact their health care provider or a local retail pharmacy like CVS or Walgreens.

Information about the COVID-19 vaccine can be found at https://coronavirus.marinhhs.org/vaccine.