After being diagnosed with covid-19 in February, spending days in a Tokyo hospital and recovering, a Japanese man in his 70s finally returned to normal life - using public transport, for example.
But after a few days of discharge, a fever came.
The elderly returned to the hospital and, to the surprise of him and the doctors, did a new test for the coronavirus that was positive.
The case, reported by NHK, a public communications company, alerted scientists because, until now, many believed that a person could not be infected with covid-19 twice - at least in the short term.
Some countries, like the United Kingdom, have even based their initial strategy to fight the pandemic on the principle of "herd immunity" - which considers a scenario in which a large part of the population would become immune after contracting the disease.