SAN FRANCISCO (CBS SF) -- For the first time since the COVID-19 pandemic began, San Francisco health care worker Charlotte Countee began feeling a sense of relief Sunday.

Shipments of the new vaccine began arriving in California late Sunday night.

Countee is a front line health care worker -- an employee of the San Francisco Department of Public Health. Lately, she has been testing people for COVID-19. She and her colleagues have been worried for months not just about their own health, but also that of their patients.

"It would be a great relief to be vaccinated, and be in the clear," she said. "I think treatment and care of patients would be better, because at this point we're all, you know, very very careful and very concerned and we can't get too close to patients, and I worry sometimes that that affects their care."

The response has been much the same for Eva Tenoila, who will be the first person to receive the vaccine at UC Davis Medical Center.

"So I'm so excited," she told CBS News. "I've been waiting for this. Like, I believe that something must be done and thankfully that vaccine is here. So I'm so excited. I'm so ready."

When asked why it was so important to her to get vaccinated, there was no hesitation in her answer.

"It's for the future," she said. "Like, can you imagine the situation right now? I don't want this to be like this forever. Like I have a 12-year-old son. You should be like socializing. Right. And as a caregiver, I witnessed the worst scenario. And I don't want that to be like, you know, I want it like there has to be something like a solution."

UC Davis Medical Center CEO Dr. David Lubarsky also was relieved.

"This is probably the most exciting day...maybe the most exciting day in the last 20 years," he told CBS News. "We have not faced something this serious in our country since probably 9-11. The number of people who are dying every single day is huge. And the vaccine is our way back, both as a society and as an economy. And our health depends on the quick distribution and vaccination of a large segment of our population."

The first shipments of the Pfizer vaccine left Michigan early Sunday for 145 distribution centers nationwide including California, where planes arrived on Sunday night.

The vaccine is heading to hospitals and other sites across the country that can store it at extremely low temperatures — about 94 degrees below zero. Pfizer is using containers with dry ice and GPS-enabled sensors to ensure each shipment stays colder than the weather in Antarctica.

In California, counties will have specific allotments that will be distributed to hospitals determined by state health officials to have adequate storage capacity, serve a high-risk health care population and have the ability to vaccinate people quickly.

But for many, the vaccines are still out of reach. The priority will be for health care workers to be inoculated first.

Gov. Gavin Newsom tweeted that a group of medical experts convened by Western states met Saturday to discuss the vaccine and confirm that it is safe for public use. Newsom said distribution could begin as early as Sunday.

Medical facilities at military bases in Alameda and San Diego will be among the first sites to receive vaccines, the U.S. Department of Defense announced earlier this month.