A new route for VietJet - direct flights from Brisbane to Ho Chi Minh City for $341 return.
Dates are August to November 2023. When you search for these, input some dates and tick the box that says 'Find the Lowest Fare'. Then, in the price grid, you are looking for the '$0" fares. You'll only pay the taxes and fees on these. FYI these only include 7kg hand luggage, plus a 2kg small item.
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Weather wise those dates are the perfect time to go, particularly if you want to get up to Hoi An and Danang. I'm currently in Danang for a month and am kind of regretting the choice, the heat is a little hotter than normal hitting 38 and humid.