National Guard Medic, Ross Davison, administers a Johnson & Johnson COVID-19 vaccine to Laurie Pearce, 52, at the drive-through vaccination site at Six Flags Hurricane Harbor (Waterworld) in Concord, Calif., on Wednesday March 31, 2021. (Ray Saint Germain/Bay City News)

Contra Costa County began offering the omicron-targeting COVID-19 booster vaccines Friday at its vaccination clinics.

Federal regulators approved the boosters manufactured by Pfizer-BioNTech and Moderna last week. Both vaccines are bivalent, targeting the BA.4 and BA.5 subvariants of omicron as well as the original COVID strain.

The Moderna booster is available to adults while the Pfizer booster is available to people ages 12 and up. People are eligible for one dose of the omicron-targeting booster if they received their last vaccine dose at least two months prior.

The new boosters will be used for all future booster vaccinations for people ages 12 and up while the original mRNA vaccines will only be authorized for initial vaccine series for those aged 6 months and up and as a booster for kids between ages 5 and 11.

Nearly 84 percent of Contra Costa County residents have completed their initial vaccination series while 54.3 percent have received at least one booster vaccine dose.

Booster vaccination appointments for Contra Costa County can be made at or by calling (833) 829-2626.

Boosters are also available via walk-in at county-run clinics in Concord, Antioch and Richmond and at retail pharmacies and standard health care providers.