A medic collects swab samples from a woman at an industrial zone in Thu Duc District, HCMC for Covid-19 testing, April 20, 2020. Photo by VnExpress/Quynh Tran.

Of the active eight have tested negative once and six twice.

Apart from eight relapsed patients under treatment, including three recorded on Monday, a discharged British man whose samples tested positive as he left Vietnam has confirmed negative again in the U.K.

Health experts have not been able to explain the relapses so far. For now, there is some speculation weak immune systems of the patients might have allowed the virus to flare up again.

The National Institute of Hygiene and Epidemiology and the Pasteur Institute in Ho Chi Minh City are cultivating viruses from relapsed patients to further study the cause of the phenomenon.

As of Tuesday morning, Vietnam had recorded 270 coronavirus patients and discharged 222.

More than 45,000 people are being quarantined and medically monitored across the country, 323 in hospitals, more than 8,400 in isolation facilities and the rest at home.

By last Friday morning, the country had gone eight straight days without a new infection, but that evening saw two new cases, both students returning from Japan. They were quarantined on arrival and are now under treatment in Hanoi.

There have been no cases of community transmission in the country since April 16.

The Covid-19 pandemic has spread to 210 countries and territories, with more than 211,200 deaths reported so far.