A Philippine government minister has tested positive for covid-19 - five months after an initial diagnosis. According to authorities experts are investigating whether he had been re-infected. Interior Secretary Eduardo Ano, was first diagnosed with COVID-19 in March, but did not show any signs of the disease at the time. On Saturday, another test returned positive. Research has shown that people infected with the virus build up antibodies starting about a week after infection or the onset of symptoms, but scientists are still unsure whether the body systematically builds up enough immunity to ward off a new attack by the virus or, if it does, how long such immunity lasts. Some studies have reportedly shown that patients who recover from this virus may lose their immunity within months, or even weeks.