"Patient 188," a 44-year-old woman from the capital city’s Chuong My District, is an employee of the Truong Sinh Company, which provides food and logistic services for several hospitals in Hanoi, including the Bach Mai Hospital, a major Covid-19 hotspot. She was confirmed positive on March 29, treated at the National Hospital of Tropical Diseases and discharged April 14 after testing negative for the novel coronavirus twice. She has been quarantined at home for another 14 days.

On Saturday, April 17, she developed a cough and felt a tightness in her chest. A subsequent test revealed that she was positive for the Covid-19 virus.

She has been taken back to the National Hospital of Tropical Diseases. Three people – her husband, daughter and the driver who took her home, have had their samples taken for Covid-19 testing. Ten others who had had contact with the three are now under quarantine, said Nguyen Khac Hien, director of the Hanoi CDC.

The woman is Vietnam's second case to test positive for the novel coronavirus after having been discharged from hospital. The other was "Patient 22," a 66-year-old British man who flew from the U.K. to Vietnam on March 2.

He was confirmed positive on March 8 and treated at the Da Nang Hospital in central Da Nang City. He was discharged March 23 after testing negative three times. After finishing a post-discharge two-week quarantine at a hotel in Son Tra District, he flew from Da Nang to Saigon for a flight back to the U.K. on April 10. Another sample was taken at the time, and it tested positive for the novel coronavirus on April 11. He had already left Vietnam by then. He has since tested negative again, U.K. authorities have said.

Cases of Covid-19 patients testing positive again after recovery are not uncommon. South Korea has reported more than 160 people relapsing.

The most likely explanation of the relapse, according to health experts, is that the test is picking up remnants of the virus. They are not certain whether those who retest positive for the virus are contagious or not.

Vietnam has confirmed 268 Covid-19 cases so far, 65 of which are active. The country has recorded no new infection in the last three days.

The Covid-19 pandemic has spread to 210 countries and territories, and the reported death toll has crossed 160,800.