Kaiser Permanente Martinez Medical Offices is one of the many locations hosting COVID-19 testing and vaccination sites around Contra Costa County, located at 200 Muir Road in Martinez, Calif. on January 13, 2021. (Samantha Laurey/Bay City News)

The number of COVID-19 cases in Contra Costa County have leveled off and the county remains in the orange tier of the state’s reopening guidelines, health officials told the county Board of Supervisors Tuesday.

The pandemic is still killing people in Contra Costa — 11 in the past week — most of whom were unvaccinated people in their 40s, 50s and 60s, county health officer Dr. Chris Farnitano said.

There have been 128 “breakthrough” cases countywide the past three months, meaning fully vaccinated people who still tested positive, with or without symptoms. One of those people — an elderly person in hospice care before testing positive — died. Four other breakthrough cases required hospitalization.

“We’ve had over 100 deaths in the unvaccinated or partially vaccinated during this time frame, the same three-month period,” Farnitano said. “That just tells you these are incredibly effective, very powerful vaccines. They’re not perfect; but they dramatically prevent cases and, even more so, hospitalizations and deaths from Covid.”

Farnitano said the West Coast variant is still the most prevalent in the county, though officials have tracked 32 cases of the U.K. variant.

“That’s concerning, because it does seem to spread more easily and cause more severe disease,” he said. Health officials expected a fourth wave of coronavirus after recent holidays and spring break, but in Contra Costa County “it’s been more of a swell or a speedbump.”

The county reported passing its goal of administering a million vaccinations by Saturday, well before its stated goal of doing so by Memorial Day. More than 630,000 county residents are at least partially vaccinated — more than 67 percent of the county 16-and-older population. More than 430,000 residents are fully vaccinated.

Information on COVID-19 in Contra Costa County can be found at https://www.coronavirus.cchealth.org/.