The second quarter saw the lowest sales this year of 518,900 due to the nationwide social distancing campaign imposed in April to curb the spread of the novel coronavirus.
Sales began to recover in the third quarter and rose 30.6 percent quarter-on-quarter to 677,700.
VAMM is made up by Honda, Piaggio, Suzuki, SYM, and Yamaha, but only Honda released sales figures.
The Japanese giant, which has an over 80 percent market share, saw April-September sales fall 25 percent year-on-year to 958,900 units.
Last year Vietnam, with sales of 3.27 million units, was the fourth largest motorbike market globally behind India, China and Indonesia, unchanged from 2018, according to Italian market research firm Motorcycles Data.