A Philippine government minister has tested positive for coronavirus five months after an initial diagnosis, authorities said Monday, as experts investigate whether he had been re-infected.

Interior Secretary Eduardo Ano, who is helping to spearhead the country’s virus response, said he returned a positive test on Saturday after experiencing flu-like symptoms last week.

He was first diagnosed with COVID-19 in March but did not show any signs of the disease at the time.

People infected with coronavirus build up antibodies starting about a week after infection or the onset of symptoms, research has shown.