All of the patients are workers at an industrial park in Chi Linh Town where the first case of Hai Duong and also one of the first cases of the ongoing community outbreak was detected.
The infections were detected following mass testing of people related to the cluster.
Before the test results arrived as positive, those 37 workers had been isolated in line with contact tracing protocols.
With the new confirmed cases, Vietnam has registered 366 domestic Covid-19 cases in 10 cities and provinces ever since infections returned to the community on January 28.
Hai Duong now has 277 cases, Quang Ninh 42, Hanoi 21, Gia Lai 14, Binh Duong four, Bac Ninh three, Hoa Binh two, HCMC, Hai Phong and Bac Giang one each.
The nation has so far recorded 1,948 Covid-19 patients and 449 are active.
More than 2.27 million people around the world have died of Covid-19 after almost 105 million got infected.