The Health Department of the central Quang Nam Province announced Friday the infected passengers landed in the Da Nang International Airport in Da Nang on four different flights.
Of them, eight were on flight VN99 from the U.S. and three on flight VN417 from South Korea that both landed on Dec. 24. Two others were on flight VN417 from South Korea on Dec. 23 and one on flight QH9451 from South Korea on Dec. 21.
They tested positive for the new coronavirus upon arrival and were sent to quarantine facilities in Quang Nam Province that borders Da Nang.
Their samples were sent to the Pasteur Institute of Nha Trang, whose genetic sequencing results that arrived on Thursday confirmed that they were infected with the Omicron, or B.1.1.529 variant.
Deputy Minister of Health Nguyen Truong Son has confirmed the information with VnExpress.
Around 700 passengers on the four flights and dozens of crew members were also quarantined upon arrival, as per Vietnam's current immigration regulations. They finished their quarantine by Friday morning.
Vietnam confirmed the first Omicron infection on Tuesday, a person arriving in Hanoi from the U.K. on Dec. 19.
Health experts have said earlier that Vietnam should beef up its healthcare system, ensuring that medical centers are well-equipped and can up their capacity, so as to avoid an Omicron-triggered overload.
A team of researchers at Hong Kong University's medicine faculty has found that the Omicron variant replicates 70 times faster in human airways than the Delta, but infection in the lungs appears to be less severe compared to the original virus strain.
Omicron's rapid replication in the airway may explain why it transmits faster than previous variants of the virus, but lower infection in the lungs may indicate that it causes less severe disease, they said.
The World Health Organization said Wednesday that the risk posed by the Omicron variant is still "very high." It said that in the week ending last Sunday, the global number of new cases rose by 11 percent compared to the previous week, while the number of new deaths dipped by 4 percent.