In 2011 vietnams population of tigers was estimated at 20. These are of the Indochinese sub species, unfortunately with only around 350 left across all countries it lives in, this sub species could still be lost. It should be noted, that the last photo was in 1997, and it is considered functionally extinct.
Given populations of tigers in nearby countries, if Vietnam improves its forest health the tiger is likely to return on its own in due course.
Unfortunately, there is little more to say about the tiger in Vietnam