The Dong is not a freely floating currency, so the state has to take the steps to devalue or revalue. Nevertheless, the long term goal is to let interest rates go up gradually, which will have the effect of tempering inflation.
The Vietnamese government, in all their infinite wisdom, now have a currency that is overvalued, with concurrent inflation caused by a huge inflow of cheap dollars. If they were smart (which obviously, they are not), they would allow the Dong to float completely.