Paola Kudacki for TIME

The sound of sirens is not unusual in New York City. But this spring, the constant wailing was almost unbearable. Luckily, there was an army of health care workers on the other end. Like Amy O’Sullivan, an 18-year veteran ER nurse at Wyckoff hospital in Brooklyn. She treated the first COVID-19 patient at the hospital, who became the city’s first death in early March, before the importance of PPE was truly understood. Amy began displaying symptoms a few days later. After she was intubated and spent four days on a ventilator, she went home to rest for less than two weeks before returning to work.

Amy is just one of the millions of health care workers worldwide who risked everything to serve others. Many moved into hotels, spare bedrooms, even garages at the height of the pandemic to protect their families. From doctors to janitors, the entire ecosystem that keeps a hospital functioning became a new kind of ground zero, their exhausted eyes conveying competence and compassion. There are two simple words for their heroism: Thank you.

Couric is an Emmy Award–winning journalist and the founder of Katie Couric Media

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