A health care worker draws a dose of the Pfizer COVID-19 vaccine. (Photo via Province of British Columbia/Flickr)

Health officers in eight Bay Area counties urged health systems Wednesday to prioritize COVID-19 vaccinations for older residents amid vaccine supply shortages in the region.

Health departments in Marin, Napa, Santa Cruz and Solano counties and their health care partners are prioritizing vaccinating all residents age 75 and older while Contra Costa, San Francisco, San Mateo and Santa Clara counties will do the same with residents age 65 and older.

The intent, according to health officers in the eight counties, is to limit coronavirus-related deaths by targeting the age demographic with the greatest risk of dying.

As of Jan. 28, an average of 83.6 percent of COVID-19 deaths in the eight counties have been residents age 65 and older.

“Three out of four COVID-19 deaths in Marin are among residents age 75 or older,” Marin County Public Health Officer Dr. Matt Willis said. “A vaccine offered to a resident above age 75 is 300 times more likely to save a life than a vaccine offered to someone under the age of 50.”

Health care workers and nursing home residents will also continue to be vaccinated in accordance with the state’s vaccine prioritization guidelines.

The region’s current pace of supply, however, could limit counties’ ability to get vaccine doses for several weeks to older adults who want them.

The two-dose nature of the vaccines currently on the market, developed by Pfizer and Modern, also makes it difficult to begin vaccinating new people, according to the counties, because portions of new shipments must be earmarked for second doses.

“We need to be direct and honest with the public that, although we want to vaccinate everyone, right now we just don’t have enough vaccine to do so,” Santa Clara County health officer and public health director Dr. Sara Cody said. “Given limited supply of vaccine, we must prioritize vaccinating those at greatest risk of death or serious illness.”

Vaccine supply has been so limited that the Centers for Disease Control and Prevention revised its vaccine guidance Jan. 21 to allow for second vaccine doses to be administered up to six weeks after a first dose, if necessary.

Second doses of the Pfizer vaccine are recommended to be administered three weeks after the first dose while four weeks is recommended for the Moderna vaccine.

“Modest delays in the administration of the second dose, if absolutely necessary, would not be expected to decrease the protection conferred by the second dose,” the CDC said in a statement.

Gov. Gavin Newsom said Wednesday that the state will receive some 1,060,000 vaccine doses this week, but the federal government lacks the amount of vaccine needed by a state of California’s size.

“We are anxious to vaccinate a much broader segment of the population, and are ready to do so as soon as vaccine supplies allow,” Cody said.