By Kenny Choi

SAN FRANCISCO (CBS SF) — In just hours, the first doses of the Pfizer COVID vaccine will be shipped from its manufacturing plant to hundreds of locations across the country including the San Francisco Bay Area.

UPS and Fed-Ex will be delivering to hospitals and other medical facilities starting early Sunday morning. The companies say some shipments will reach locations within a day.

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That means those at the top of the list to get vaccinated could be getting shots as early as Monday.

But with San Francisco hospitals just getting 12,000 doses combined in the first shipment, those shots will mostly only be given to front line health care workers. The vaccine needs to be administered in two doses. A second batch of vaccine was expected to arrive within 21 days for those second doses.

During the shipping process, every UPS and Fed-Ex truck carrying vials of the COVID vaccine will have a device that tracks its location, temperature, light exposure and motion.

“Make no mistake, distribution has begun,” said Chief Operating Officer of Operation Warp Speed General Gus Perna. “Right now, boxes are being packed and loaded with vaccines with emphasis on quality control.”

But delivery is not without its perils.

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“What concerns me is that there’s so many different routes and so many different rollouts,” said UCSF Professor of Medicine Infectious Disease Specialist Dr. Peter Chin-Hong.

Many hospitals say they still don’t know exactly how many doses they’ll receive, or when the shipments will arrive.

“We do encourage you to take the vaccine, because it will make a difference not only for you, but also for other people in the community, including your family, including your friends, but also the wider community,” said Stanford Professor of Epidemiology Dr. John Ioannidis.

The arrival of the COVID vaccine sounds like the cure-all for many, but a recent Pew Research Center poll finds 18 percent of Americans would “definitely not” take the vaccine, “if it were available today” and that 21 percent say that they would “probably not.”

“Minority populations in particular have been a little bit more hesitant, given the history of research and interventions,” said Hong.

]Data from the FDA, shows the Pfizer vaccine to be 95 percent effective. A booster is needed three weeks after the initial injection.

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Starting December 21, CVS and Walgreens will start sending out teams to approximately 75,000 nursing homes and other long-term-care facilities across the country.