It had been over a month since Mirabai Nicholson-McKellar was infected with the coronavirus, and the 35-year-old filmmaker thought she was on her way to recovery. Then the shortness of breath came back, followed by chest pains.

A visit to the emergency room and a second test for Covid-19 gave another positive result. Just three days earlier, she’d been cleared by health authorities in Australia’s New South Wales state, and was allowed to end her home quarantine after going 72 hours without symptoms.

“When is this going to end? I think about that constantly,” she said of the twists and turns in her health. “Am I still contagious? How do I know if I’m not contagious?”

Her experience adds to a growing number of reports of patients appearing to have a reactivation of symptoms, testing positive again, or even potentially being reinfected. Such incidents don’t align with the generally accepted understanding of how virus infections work and spread.