The latest move follows the relapse of 10 patients who were discharged from hospitals after they had tested negative for the novel coronavirus at least twice. One of them, a British man, has flown back to the U.K. and tested negative there, while the other nine have been sent back to hospitals in Vietnam for further monitoring.

The latest relapse, recorded Tuesday, is "Patient 151," a Brazilian woman in Ho Chi Minh City. She was discharged on April 18 but tested positive 10 days later. She has been transferred to the Cu Chi field hospital in the city.

Her husband, "Patient 207," a Brazilian man, also relapsed two days earlier.

Three other relapses are in Hanoi, two in the northern province of Quang Ninh, one in the south central province of Binh Thuan, and another in HCMC.

The nine relapses are among 49 active patients in Vietnam, while another 221 have been discharged and healthy.

The ministry has further said that in case patients refuse to stay back at hospitals, health authorities in their localities have to make sure that their houses are qualified enough for safe quarantining at home.

If the local authorities feel that the situation is not safe for the patient to be quarantined at home, he/she will be taken to healthcare centers in their localities.

For either option, the recovered patients will be tested again at least two times, at the end of the first and second weeks. All tests will use the real-time PCR method, widely considered the most accurate for the novel coronavirus. In most cases, initial rapid test results will be double checked using this system.

All relapsed patients will be quarantined and treated as new Covid-19 patients. Samples taken from them will be sent to the National Institute of Hygiene and Epidemiology and the Ho Chi Minh City Pasteur Institute where the viruses are being cultivated and studied to see if they can be transmitted to others.

On Tuesday, the Health Ministry said that the virus taken from five of the relapse cases was inactive, which means it's very unlikely that the patients can spread the disease to others.

So far, Vietnam has allowed all recovered patients to go home immediately, and foreign visitors to quarantine themselves in qualified accommodations like hotels. During the 14-day post-discharge quarantine, their health is monitored every day by medical staff.

Health experts have yet to identify reasons for Covid-19 relapses. The Health Ministry said earlier that the weak immune systems could be a cause, allowing the virus to stay on.

Other countries in the world have also reported Covid-19 relapses. In South Korea, at least 222 people have tested positive for the virus again after recovering. China and Brunei have reported relapses too.