Vietnam's Health Minister Nguyen Thanh Long described the latest mutation on Saturday as "very dangerous".
Viruses mutate all the time and most variants are inconsequential, but some can make a virus more contagious.
Since COVID-19 was first identified in January 2020, thousands of mutations have been detected.
"Vietnam has uncovered a new COVID-19 variant combining characteristics of the two existing variants first found in India and the UK," Mr Nguyen told a government meeting, according to Reuters news agency.
