The 21-year-old man had returned to Vietnam from Russia on August 10, tested positive for the virus on August 25, and was treated at the National Hospital for Tropical Diseases in Hanoi.

After being discharged in mid-September he isolated himself at home for two weeks.

On November 7 he went to the Transport Hospital with a fever and was given medicines for a viral infection.

On November 14 he had a 39-degree fever and felt fatigued. He returned to the hospital and had a novel coronavirus test done, testing positive. He is again at the National Hospital for Tropical Diseases for treatment.

A PCR test conducted by the tropical diseases hospital on Monday morning showed he was negative with the virus.

Authorities have yet to make any conclusion.

A preliminary investigation found 25 people had been in close contact with him, including his grandmother, father and brother in Cau Giay District.

The woman has been isolated at home, the brother is on an overseas trip and the father is at the National Hospital for Tropical Diseases.

Another person who had been in close contact with him is self-isolating at home in Ha Dong District, while another person from Dong Da District who visited him at the hospital on November 14 has yet to be traced.

The Transport Hospital found 20 people who had been in contact with him, and isolated 17 of them and has taken their samples for testing.

Vietnam has had 1,281 Covid-19 cases so far, 140 of them active. Thirty five have died, most of them elderly people with underlying conditions like diabetes and kidney failure.

No local transmission had been recorded in over two months.

Hanoi had gone three months without a local case.