Just after 9AM on Monday, Sandra Lindsay, a critical care nurse in Queens, New York, was vaccinated against COVID-19. Lindsay was one of the first people in the United States to get a dose of the newly authorized Pfizer and BioNTech vaccine and was the first to get the shot in New York, an early epicenter of the pandemic.

“I hope this marks the beginning of the end of a painful time in our history,” she said.

Lindsay was vaccinated just two days after the Food and Drug Administration issued an Emergency Use Authorization (EUA) for the Pfizer and BioNTech product. The announcement marked the end of a record-breaking push to develop a vaccine against the deadly disease and the start of an unprecedented campaign to vaccinate millions of people in the US.

As soon as the authorization was handed down, Pfizer’s factory started preparing doses for shipment. Trucks left the company’s Michigan facility on Sunday, headed for the airport.

Shipments touched down all over the country this morning, and other health care workers joined Lindsay as the first group of vaccine recipients. Ohio State University Wexner Medical Center coordinated the first shots after a countdown of “three, two, one, vaccinate.” Staff at Hartford HealthCare in Connecticut got their first doses at an outdoor tent, surrounded by cameras and reporters.

Other hospitals will take a few more days to begin vaccinations. Boston Medical Center plans to start Tuesday or Wednesday, for example. Some doctors said on Twitter that they still haven’t gotten information about when their shots will be scheduled.

The FDA is expected to authorize the Moderna COVID-19 vaccine at the end of this week, and if it does, shipments of that product will start to roll out across the country as well.

Operation Warp Speed, the federal partnership behind vaccine development, said that 20 million people could be vaccinated against COVID-19 by the end of the year. Some hospitals say that seems unrealistic because of the logistical challenges of coordinating shots and shifting expectations around the number of doses they’ll receive.

Despite all efforts to accelerate the distribution of the vaccine, COVID-19 cases are still surging around the country. It’ll be a few months before the vaccine is able to slow down the spread of death and disease. Still, the first injections are a scientific triumph — and for many people in the US, they are a bright sign of hope at the end of a long, dark year.