the thing is , like stock charts they are not forward predictive when flat as long people are still active. each step up just means that another cluster is happening. So your question is , how far out do I go before I become reasonably sure that one more case is not going to come into town?
If ten infected chinese walked into Hanoi tomorrow and are not quarentined, you would see the case load in hanoi start going up again.
If they do not come from the outside, and there is good reporting from all hospitals, then it is very unlikely there will be more cases in Hanoi.
That is why draconian quarentine measures help. And a little less lethal mutation grows out and it becomes a bad cold