The first shots were given in the American mass vaccination campaign Monday, opening a new chapter in the battle against the coronavirus pandemic, which has killed more people in the United States — over 300,000 — than in any other country and has taken a particularly devastating toll on people of color.

Shortly after 9 a.m., the new Pfizer-BioNTech vaccine was administered in Queens, New York, the first known inoculation since the vaccine was authorized by the Food and Drug Administration late last week. It was a hopeful step for New York state, which the pandemic has scarred profoundly, leaving more than 35,000 people dead and severely weakening the economy.

“I believe this is the weapon that will end the war,” Gov. Andrew Cuomo said Monday morning, shortly before the shot was given to Sandra Lindsay, a critical care nurse and the director of patient services in the intensive care unit at Long Island Jewish Medical Center. State officials said the shot was the first to be given outside of a vaccine trial in the United States.

Lindsay, who has treated patients throughout the pandemic, said that she hoped her public vaccination would instill confidence that the shots were safe.

“I have seen the alternative, and do not want it for you,” she said. “I feel like healing is coming. I hope this marks the beginning of the end of a very painful time in our history.”

President Donald Trump posted on Twitter: “First Vaccine Administered. Congratulations USA! Congratulations WORLD!”

Shortly afterward, Mayor Bill de Blasio of New York City said at a news conference that “To me, we were watching an incredibly historic moment, and the beginning of something much better for this city and this country.”

While the first dose of the vaccine was administered in New York, people across the nation began receiving it Monday as well. There was plenty of applause and some tears as news cameras captured the mundane rituals of an injection, underscoring the pent-up hope that this was the first step in getting past the pandemic.

“Today is the first day on the long road to go back to normal,” Mona Moghareh, a 30-year-old pharmacist, said after administering the first dose at a hospital in New Orleans.

But the joy was tempered by the harsh reality of the devastation the virus continues to inflict. The United States surpassed 300,000 virus-related deaths Monday, and cases continue to surge across the country.

The vaccinations started after the Food and Drug Administration’s emergency authorization of the Pfizer-BioNTech vaccine Friday night.

On Sunday, trucks and cargo planes packed with the first of nearly 3 million doses of coronavirus vaccine had fanned out across the country, as hospitals in all 50 states rushed to set up injection sites and their anxious workers tracked each shipment hour by hour. But the rollout is less centralized in the United States than in other countries that are racing to distribute it.

According to Gen. Gustave F. Perna, chief operating officer of the federal effort to develop a vaccine, 145 sites were set to receive the vaccine Monday, 425 on Tuesday and 66 on Wednesday. There appeared to be few logistical problems, though Puerto Rico received half the number of doses it expected, and had to scramble to adjust its distribution plan. The remaining doses are expected to arrive Tuesday and Wednesday.

A majority of the first injections given Monday are expected to go to high-risk health care workers. In many cases, this first, limited delivery would not supply nearly enough doses to inoculate all of the doctors, nurses, security guards, receptionists and other workers who risk being exposed to the virus every day. Because the vaccines can cause side effects including fevers and aches, hospitals say they will stagger vaccination schedules among workers.

Lindsay emphasized the symbolic importance that she was the first American to receive the vaccine — as a Black woman, she is among the demographic most disproportionately devastated by COVID-19. African Americans also have long been subjected to unethical medical research, raising some concern that they may be more hesitant to take the vaccine.

“I want people who look like me and are associated with me to know it’s safe,” she said. “Use me as an example. I would not steer the public wrong.”

Residents of nursing homes, who have suffered a disproportionate share of COVID-19 deaths, are also being prioritized and are expected to begin receiving vaccinations next week. But the vast majority of Americans will not be eligible for the vaccine until the spring or later.

In an interview with MSNBC on Monday, Dr. Anthony Fauci, the nation’s top infectious disease expert, laid out a timeline for a return to normalcy that stretched well into 2021. He stressed that until then, social distancing and masks will remain crucial in the fight to stop the spread of the virus.

He predicted that the average person with no underlying conditions would get the vaccine by the end of March or beginning of April. If the campaign is efficient and effective in convincing people to get the vaccine, most people could be vaccinated by late spring or early summer, he said.