Vietnam confirmed one domestic COVID-19 case on Wednesday morning, with the confirmation given only after the fourth test.
The 22-year-old patient was registered in northern Bac Giang Province, the Ministry of Health said.
He started to be quarantined on February 1, when his wife was recorded as patient 1,820.
He had tested negative for the coronavirus three times before his fourth test came back positive on Tuesday.
The patient is being isolated for treatment at the National Hospital for Tropical Diseases in Hanoi.
The Ministry of Health announced 16 local infections on Tuesday.
Vietnam has detected 2,070 coronavirus cases since the virus first hit it on January 23, 2020.
A total of 1,177 cases were locally transmitted while 1,474 patients have recovered from the respiratory disease. Thirty-five have died of the pathogen, most having suffered underlying medical problems.
Four hundred and eighty-four of the local infections have been logged in 13 provinces and cities since a new wave struck the country on January 28, including 327 in Hai Duong Province, 53 in Quang Ninh Province, 28 in Hanoi, and 33 in Ho Chi Minh City.
The risk of further community spread stays extremely high in Ho Chi Minh City because the virus has hit Tan Son Nhat International Airport, with the source of infection still unknown, health authorities said.
The health ministry has established a task force led by Deputy Minister Nguyen Truong Son to help the city suppress the new round of infections.
The whole country is on high alert as droves of people are flocking back to their hometowns from urban centers for the Lunar New Year holiday this week.
Vietnam is quarantining nearly 100,000 people who either had contact with infected patients or entered the Southeast Asian country from virus-hit regions.
The nation is sealing its borders to all international arrivals but it still allows entry to skilled workers, experts, diplomats, and Vietnamese repatriates, who are all subject to mandatory quarantine upon arrival.
The health ministry gives daily updates on patient counts at 6:00 am and 6:00 pm.