Scientists in Hong Kong are reporting what appears to be the first confirmed reinfection of a novel coronavirus patient—a development which suggests immunity to the virus could only be temporary. “An apparently young and healthy patient had a second case of COVID-19 infection which was diagnosed 4.5 months after the first episode,” University of Hong Kong researchers said Monday in a statement reported by The New York Times. If accurate, the findings suggest that people who recover from a COVID-19 infection may only have immunity to the novel coronavirus for a few months. “Our results prove that his second infection is caused by a new virus that he acquired recently rather than prolonged viral shedding,” said the university’s Dr. Kelvin Kai-Wang.

Doctors have previously reported cases of presumed reinfection—including in the United States—but none of those cases were confirmed through scientific testing, according to the Times. The development could have implications for vaccines being developed around the world for the virus.