Phan Trong Lan, director of the Pasteur Institute in Ho Chi Minh City, made the announcement after reports got out that a Nigerian passenger had entered Vietnam on Tuesday with fever and went undetected by thermal imaging cameras set up at Tan Son Nhat International Airport.
The passenger took fever relief medicine six hours before arriving at the airport, Lan said.
Although the man was not detected by the cameras, he was quarantined by Vietnamese health officers for a medical checkup.
He was among 20 Nigerian passengers who were required to undergo medical screening as soon as they arrived at the airport.
The man wrote on a health declaration form that he had sore throat, and had taken a fever relief pill.
He was then kept at the airport for 10 hours and discharged after he his fever failed to return.
Vietnamese health officers made a list of all the 20 passengers with their contact addresses and phone numbers so they could monitor them for 21 days.
Two other fever Nigerian men sent to the HCMC-based Hospital for Tropical Diseases on Tuesday evening for isolation were discharged from hospital Wednesday evening as they are not having fever and have no Ebola-like symptoms, said a health ministry spokesman.
Nguyen Van Vinh Chau, the hospital director, said many passengers took fever relief medicine to avoid being detected by cameras at airports as they didn't want to be bothered.
Fever relief medicine is effective for around 8-12 hours against normal fevers and flu, he said. But such medicine would only prove effective against fever caused by the Ebola virus for an hour or less.
A person infected with Ebola virus suffers high and continuous fever that grows progressively worse by the hour, according to Chau.

Vietnam has beefed up mandatory temperature checks at its two major international airports in Hanoi and HCMC in a bid to prevent passengers bringing the deadly virus into the country.

Newswire AFP quoted the World Health Organisation as saying Thursday that the latest official toll from Ebola has jumped 106 in two days to 1,350 dead, with the bulk of cases in Liberia, Guinea and Sierra Leone.

In Myanmar a local man is still undergoing tests after arriving from Guinea with a fever, it said.

​Source: Thanhniennews