They were all placed in quarantine as soon as they landed in Vietnam, therefore they could not pose any threat to the community, health officials assured.
One of the newly detected patients, a 37-year-old woman of the Philippines is an education expert. She took flight QH9461 from the Republic of Korea to Phu Quoc Airport in Kien Giang province, southern Vietnam, on July 19.
She tested positive for the virus on July 20 and was transferred to the Phu Quoc District Medical Centre for medical observation and treatment.
The other three patients are Vietnamese, living in Hung Yen, Phu Tho and Quang Binh provinces.
They boarded aircraft VN5062 from Russia to Van Don International Airport in Quang Ninh province on July 17.
They first tested negative the same day but second tests on July 22 showed they were infected with the virus. The test results were confirmed on July 23 by the National Institute of Hygiene Epidemiology.
The three patients are being quarantined at the Nam Dinh provincial General Hospital for treatment.
The four new patients brought the total number of coronavirus infections in the country to 412. No deaths have been reported.
Of the total, 365 patients have fully recovered and have been discharged from hospital, representing 88.6%.
According to the Ministry of Health, Vietnam has gone through 98 days in a row without new locally transmitted coronavirus infections.