The middle-aged patient had been battling coronavirus for months. Doctors had provided the antivirus needed to fight Covid-19, medications to alleviate blood clots, immune modulators to attempt regulation of out-of-control immune responses and steroids to counteract inflammation.

He’d been struggling to recover on and off at home. His blood oxygen levels would decrease even though assessments indicated that he had tested negative for the virus.

Dr. Jonathan Li runs a laboratory at Boston’s Brigham and Women’s Hospital evaluating viruses such as HIV and its mutations. He was also called in to help research what was happening to the patient.

Turns out it was just what doctors both knew and were afraid would happen — the virus was mutating the patient’s body.