Applying for another visa

Hi there,

I will be travelling to Vietnam twice in September.
I currently have a visa stamped on my passport organized by work.
My current company sent my passport to the embassy and got a single entry visa stamped.
Shortly after the first visit, I will be travelling again to Vietnam for holiday.
Can I apply for another single entry visa while I already have a single visa on my passport?
Or should I wait until I make the first visit and apply for another one after I use the current visa?

Thank you.