Chung, a native to the northern province of Thanh Hoa who worked in Guinea for two years, returned to Da Nang on Friday after going through Morocco, Qatar, and Ho Chi Minh City.
He was admitted to Da Nang Hospital Saturday afternoon after showing Ebola-like symptoms of headache and high fever. Initial test results on him are positive for malaria.
Yen said the lesson learned from this case is "screening at airports and ports must be further tightened."
"Just a mistake in screening which lets Ebola-infected people into Vietnam will leave the public health sector in huge difficulty in order to prevent or control the disease," she said.