The Ministry of Health said this was the first time in 26 days the number of people classified as potential carriers had dropped to around 300.
It had been more than 1,600 on Wednesday, the lowest in 20 days.
Those deemed Covid-19 suspects are people who came into close contact with patients or returned from outbreak areas, and have symptoms like cough, fever and shortness of breath. They are quarantined in hospitals spealized in Covid-19 treatment.
Rapid testing has allowed medical workers to identify suspected cases in the community. Many public hospitals and some private ones have been authorized to carry out the tests.
The highest number of suspected cases since the pandemic broke out in the country in late January was on April 1 when there were 4,617.
As of Thursday morning in Hanoi over 1,100 people are being quarantined at centralized facilities for coming from infected areas or having had close contact with patients, while 11,000 others are being monitored in the capital city.
In HCMC more than 200 people are in quarantine camps and nearly 200 are quarantined at home.
The government announced on Wednesday that the social distancing campaign would continue until April 22 in Hanoi, HCMC and 10 other localities deemed to be at high risk - Lao Cai, Quang Ninh, Bac Ninh, and Ninh Binh provinces in the north; Da Nang City and Quang Nam, Binh Thuan, Khanh Hoa, and Ha Tinh provinces in the central region; and Tay Ninh Province in the south.
Vietnam’s Covid-19 count as of Thursday was 268, with 97 people still in hospitals. The remaining 171 have been discharged.
Most of the patients under treatment are in stable condition, with 13 testing negative for the new coronavirus once and eight twice.
Three are in critical condition, and require ventilators and blood filtration.
The pandemic has claimed over 134,300 lives and spread to 210 countries and territories.