"Patient 1451," 23, is being treated at the Cu Chi field hospital in Ho Chi Minh City after test results Sunday showed he was positive for the virus.
This man had stayed with a 32-year-old man, "Patient 1440", in Myanmar for three months. The two men later visited Thailand and Cambodia before crossing borders to enter Vietnam illegally with four others in a seven-seater car.
Back in HCMC, the 23-year-old man, now "patient 1451," returned to his apartment on Su Van Hanh Street in District 5 and made contact with many people. He came to a hotel, a karaoke palor, restaurants, cafes, VPBank in Binh Chanh District and a MobiFone branch in District 5.
Four apartment blocks or 72 apartments at his residential area have been locked down after his diagnosis.
Thirteen F1 (people having close contact with "patient 1451") and 48 F2 (people having close contact with F1) have been isolated for monitoring.
"Patient 1440" is being treated in Vinh Long Province.
Authorities have identified four others in the group of six. Two of them have tested negative for the virus, and one has been isolated while waiting for test results.
They are still searching for the last one, a man named Kha in District 9. Nguyen Tan Binh, director of HCMC's Health Department, said Kha is "the most worrying case".
At an online conference with city and provincial leaders Monday, Prime Minister Nguyen Xuan Phuc urged people across the country to report any case of people illegally crossing borders to enter Vietnam. He said everyone should be vigilant about such entries because they are a major source of infection.
Vietnam also recorded nine imported cases from Russia on Monday.
The country’s current Covid-19 tally stands at 1,451 cases, with 35 deaths.
Fifteen recoveries were confirmed Monday evening. No community transmission has been recorded nationally in nearly a month.
As part of existing Covid-19 prevention measures, anyone who wish to enter through the Vietnamese border must report their entry to border guards, and be quarantined immediately.