SAN DIEGO — County leaders have moved up the vaccination start date for a new group of residents — including teachers, police and farm workers — to Saturday.

The vaccine will be available to those Phase 1B recipients at sites around the county, though Supervisor Nathan Fletcher warned that it is a group of an estimated half a million people in the region, and not everyone will get an appointment in the opening weeks.

Fletcher said a “slack” in demand for first-dose appointments among the 65-and-up crowd led the county to open up to the larger group a bit sooner than the original plan of Monday.

The new tier of recipients includes agriculture and food workers, education and child care professionals and non-health care emergency services workers, such as law enforcement officers. Fletcher said a detailed breakdown would soon be available on the county’s website.

School staff from K-12 campuses will have a designated provider, VEBA, and doses are being held specifically for those educators. The county says it will set aside twice the state’s recommended 10% of vaccine doses for school staff, reserving 20% as many San Diego schools gear up to bring kids back on campus in April.

Law enforcement will receive the vaccine through a Scripps Health program, and farm workers will get shots from Cal Fire, which will meet workers where they are in many cases to administer the vaccine.

People working in other forms of child care and in higher education will go through the county’s main vaccine appointment portal, along with other members of Phase 1B who do not have a specific provider designated by the county.

Regional case rates have been declining at an encouraging rate, officials said Wednesday, signaling a potential drop in the near future to the red tier of the state’s reopening plan. The county reported 658 new COVID-19 infections Wednesday and 12 additional deaths, increasing the cumulative totals in the county to 258,463 cases and 3,230.

The county’s adjusted rate of daily new COVID-19 cases dropped to 15 per 100,000 residents, according to state data released Tuesday. The county is still in the most restrictive purple tier of the state’s four-tier economic reopening system.

To move out of purple and into the less restrictive red tier, the county’s new case rate must drop to seven per 100,000 residents. The county’s seven-day average positivity rate already qualifies for the red tier, at a state-adjusted 5%, but the county must meet all required metrics before advancing out of the purple tier.