Regarding this issue, the Vietnam Social Insurance provided the following response:

Based on the regulations stated in Article 2, Clause 1 of the Social Insurance Law 2014, Vietnamese citizens who work under indefinite-term labor contracts, fixed-term labor contracts, seasonal contracts, or specific contracts lasting for at least one month, as well as enterprise managers who receive wages, are mandatory participants in social insurance.

In the case of Mr. Tuan, if he has already received social insurance once and continues to work, falling into one of the aforementioned categories, he is considered a mandatory participant in social insurance.