Less simple to handle, ironically, has been the wave of attention that has fallen on her, reflecting the global eagerness for a chink of light in such dark times. The TV interviews were fine. It was the deluge of messages of support and encouragement from members of the public that left her more stumped.

More than a thousand of them have come in on Facebook and Instagram. "We're praying for you," "we need a vaccine," "thank you for putting your life on the line".

"That has been overwhelming and humbling," Ms Haller said. "And actually, for a while, it was difficult to know what to do with all that attention, the positivity that was coming at me."

Her children – 16-year-old son Hayden and 13-year-old daughter Ellison – had no such qualms. "They thought it was pretty cool," Ms Haller said. "They would report back to me how many TikTok views I would have and what's on Reddit. They think it's hilarious."

Her efforts have even not gone unnoticed by the US President, or at least those close to him. There has been no message from Donald Trump, Ms Haller said, but a more on-brand nod to her involvement.

Footage of her taking the injection has featured in a new 30-second campaign advert touting his leadership during the crisis. She admitted, diplomatically, to being "taken aback".

Ms Haller's involvement, and that of the trial's other 44 adults taking part, is only just beginning. Her second dose is due next week. Monitoring will not end until Spring 2021. She remains confident that a successful vaccine will emerge, whether from her trial or the ones pushing forward in other corners of the world.

"Whenever we get to the vaccine, whatever it ends up being, I will be proud to have been part of the process," she said.

As for any praise, she says it is the "hundreds of thousands" of people putting their lives on the line by carrying on with their jobs – healthcare workers, store employees, farmers and janitors – who really deserve it.

"That humility is genuine," she said. "This is one thing I can do, and I'm happy to do it. I'm not saving the world." Others may disagree.