Haller, 43, the first person to receive the vaccine, was wearing a tank top when a pharmacist, sheathed in gloves, a mask and protective eye gear, injected her with an experimental vaccine named mRNA-1273. It made her arm a bit sore, “but besides that, no, no side effects,” she says.

With the outbreak rapidly spreading across the nation, Haller says she was excited to enroll in the Phase 1 trial, which started Monday.

“I wanted to do something because there’s so many millions of Americans that don’t have the same privileges that I’ve been given,” says Haller, who now works from home for a small tech company. “They’re losing their jobs. They are concerned about paying bills, feeding their family.”