https://www.scientificamerican.com/article/what-covid-19-reinfection-means-for-vaccines/

The question of whether we can be reinfected with COVID-19 has been resolved. In August, genome sequencing confirmed that a 33-year-old man in Hong Kong had indeed been infected by the same virus a second time. So too was the case for a 25-year-old man in the United States, though the originating case study has yet to be peer reviewed.

This strengthens earlier reports that have surfaced periodically throughout the pandemic. Most were in China and South Korea, and some in the U.S. None of these were ever verified in laboratory, leaving open the possibility that false positives or negatives had simply confounded test results. A new surge of similarly anecdotal reports is cropping up across Europe and India.