The first phase of the COVID-19 vaccine distribution program is well underway in Santa Clara County, which could move to the second phase as soon as the end of January, health leaders said during a Friday press conference.

They also outlined how people will be able to get the vaccines and announced a new website, sccfreevax.org, with more information.

Health care workers and residents of long-term care facilities who qualify for the first phase of the rollout (Phase 1A) are receiving the initial batches of vaccines. The doses from Pfizer-BioNTech and Moderna confer a 95% immunity from the deadly coronavirus, according to the Centers for Disease Control and Prevention.

Santa Clara County has a current allotment of 110,000 vaccine doses, with more expected, said Dr. Marty Fenstersheib, the county's COVID-19 testing officer. The county has 140,000 health care personnel who are eligible for the first round and about 47,000 have already been vaccinated. Out of 6,000 skilled-nursing facility staff, roughly half also have received the vaccine since it arrived around Christmas, Fenstersheib said.

The number of people who have actually been inoculated in the county is higher, however, since the total doesn't account for additional vaccines administered through the federal Veterans Administration health care system and long-term care facilities, he added.

There could potentially be up to 6,000 vaccinations per day by next week, according to county Supervisor Otto Lee.

County Health Officer Dr. Sara Cody said health leaders will open up the vaccines to people in subsequent phases as soon as all eligible persons in a phase are determined to have received the shots.

When Phase 1B opens up, the county will make the doses available to more people in two tiers: Tier 1 would focus on people ages 75 and older, and workers in education, child care, emergency services, food and agriculture. Phase 1B Tier 2 would include older adults ages 65 and older; workers in transportation and logistics; members of industrial, residential and commercial sheltering facilities and services; critical manufacturing employees; incarcerated individuals and homeless people, according to state health officials.

Health care workers can currently receive the vaccines through their health care provider, including Stanford Health Care, Palo Alto Medical Foundation, Kaiser Permanente and county facilities, Fenstersheib said. The county also is rolling out mass-vaccination centers and currently has three, with a goal to open a fourth next week, said Dr. Jennifer Tong, associate chief medical officer for Santa Clara Valley Medical Center.

Cody said the county is aiming for 85% herd immunity, which has been described by Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, to protect the population. While some people are already protected because they had the infection, Cody said they still recommend everyone to be vaccinated. Even after receiving the doses, people will need to keep wearing their masks, practice social distancing and take other measures necessary to protect their families and others from infection. Even if they have immunity, they could still be carrying the disease, she said.

By her estimate, about 1.5 million people in Santa Clara County would need to be vaccinated to reach the 85% level.

"We are still in an extraordinarily difficult place" regarding the number of infections spreading throughout the county, she said. Currently, the county is averaging 1,200 new COVID-19 cases per day. Countywide, more than 800 people have died since the virus emerged and the number of available intensive care unit beds is now only 20 to 25 as of the last several days, she said.

"Vaccination is absolutely central to working our way out of this pandemic. We are going to be in a transition period over the next several months," she said.

The health leaders said the vaccine rollout has been somewhat slowed by the strategic complexity of various federal protocols for the two existing vaccines; the stringent requirements, such as deep freezing; the logistics of setting up vaccine clinics near freezers; and fear among the public of the vaccines' safety.

As more people are vaccinated and people see there are relatively few adverse reactions, health leaders are hoping they will increase vaccination rates, they said. The county also keeps track of adverse reactions through the Vaccination Adverse Reaction Reporting System.

The steep spike in infections and the holidays also have contributed to the difficulties, they said. Cody added that the key unknown is what bump they will see in cases in the weeks after the Christmas and New Year's holiday travel.

When county leaders were asked how confident they were in receiving additional vaccine supplies, Fenstersheib said there's no reason to expect the county won't get the needed doses.

"We have no control over the federal government," he said, but added that when President-elect Joe Biden's administration takes power after Jan. 20, they have already committed to ramping up vaccine resources.

Watch the full press conference here:

Find comprehensive coverage on the Midpeninsula's response to the new coronavirus by Palo Alto Online, the Mountain View Voice and the Almanac here.