Do I need to apply for another visa?

Hello,

I have already been approved for a single entry visa and I am currently in Vietnam, travelling around for 2 weeks. I then fly out to Bangkok and Singapore and then I transit back through Ho Chi Minh on the 27th February 2020 before flying out to Tokyo. I will not be leaving Ho Chi Minh airport but because I will be flying in with one airline and flying out with another, I will need to go through immigration and then check back in again. Do I need to apply for another visa or should my already approved single entry visa be okay? It is valid till the 4th March 2020. Otherwise please advise if I am require to apply for another single or multi entry visa?

Thank you,
Vanessa