The U.S. returnee is a 58-year-old woman residing in Ho Chi Minh City. Her repatriation flight landed at Van Don airport in the northern province of Quang Ninh on July 16 and she was quarantined in the nearby Hai Duong Province. Tests confirmed she was infected on Tuesday.
She is being treated at Hai Duong Hospital for Tropical Diseases.
The Russia returnees are men between 24 and 45 years of age.
They returned from Russia via Belarus transit on July 17 and landed at Van Don Airport. They were quarantined in northern Hoa Binh Province and also confirmed infected on Tuesday.
The four are being treated at Hoa Binh General Hospital.
Twelve other passengers on the same Russia flight were confirmed infected with Covid-19 on Tuesday.
With Wednesday additions, Vietnam now has 36 active patients, with 365 others having recovered.
The country has not reported any case of community transmission of the Covid-19 for more than three months now.
All of its new patients are foreigners or Vietnamese repatriates who were quarantined upon arrival. Vietnam has brought home nearly 14,000 people since the pandemic broke out.
Worldwide, 618,398 people have died of he disease.