Sandra Lindsay, a critical care nurse from Northwell Long Island Jewish Medical Center was the first vaccinated in New York at 9:23 a.m. during a livestreamed event with Gov. Andrew Cuomo.
Lindsay, who lives in Queens, one of the hardest hit counties in the country, told the governor she wanted to instill trust in the vaccine.
"I believe in science. As a nurse, my practice is guided by science and so I trust that," she said during the livestream. "What I don't trust is that, if I contract COVID, I don't know how it would impact or those who I come in contact with, so I encourage everyone to take the vaccine."
Elected officials and state health leaders in different states, including Connecticut, Iowa, Florida and California, also welcomed the shipments and first shots Monday.
"First COVID vaccination in MS - proud and privileged," Dr. Thomas Dobbs, Mississippi's state health officer, said in a tweet that included a photo of his bandaged shoulder.
The rollout comes less than a week after the U.S. Food and Drug Administration authorized the vaccine for emergency use for Americans over 16. The order from the FDA led to the pharmaceutical company shipping 2.9 million doses to 636 sites across the country.
Pfizer, which produced the vaccine alongside German company BioNTech, began shipping the doses from its Michigan warehouse Sunday directly to those sites, which were pre-selected by governors and local health officials.
Pfizer said it would roll out a second batch of 2.9 million doses shortly after the first batch. The U.S. government is opting to keep 500,000 doses in reserve to address any shipping or distribution mishaps.
The vaccine, which requires two doses for full inoculation, began distribution in the United Kingdom last week.
The vaccine is the first in the country to use the genetic technology mRNA instead of viral components. Pfizer claimed its trials showed the vaccine was 95% effective at preventing symptomatic COVID-19.
The FDA will hold a hearing on Dec. 17 with Moderna, which also developed an mRNA-based vaccine, before possibly giving emergency authorization for its deployment.
According to the World Health Organization, there are 52 COVID-19 vaccines in human trials, and 162 vaccines in preclinical development.
The vaccine developments come as the U.S. is in the midst of the deadliest period of the pandemic, according to health data. America leads the world with over 16 million cases and close to 300,000 deaths, according to Johns Hopkins University's Coronavirus Resource Center.
The seven-day averages of new daily cases, 211,494, hospitalizations, 106,656, and deaths, 2,427, were at record highs on Dec. 13, according to health data from the COVID Tracking Project.
ABC News' Arielle Mitropoulos, Sony Salzman and Eric Strauss contributed to this report.
This report was featured in the Monday, Dec. 14, 2020, episode of "Start Here," ABC News' daily news podcast.
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