Don't have problem if China donated 5 millions additional doses to Vietnam or any countries in need to fight coronavirus. However, it is just a thankless gesture. Vietnam government and Vietnamese people wouldn't appreciate it, and demonize of Chinese vaccines wouldn't stop.
In previous donation, Vietnam didn't honor its promise by refusing to vaccinate Chinese in Vietnam first or vaccinate Vietnamese near the border first until China filed a formal complaint. Vietnam is the only country that required diplomatic pressure to honor its promise.
In addition, Vietnam has reject donation until now and never placed any orders for Chinese vaccines. I think if it is given a choice, Vietnam wouldn't ask for donation. Furthermore, these 5 millions doses supposed to be a sales order but now Vietnam demanded these vaccines to be donated.
Vietnam has placed an order of 51 millions doses of Pfizer, 40 + 20 millions doses of Sputnik, and 30 millions doses of AstraZeneca. But at the moment, Vietnam has not placed any order of Chinese vaccines except demanding donation. Donating to a nation that you know would bite your hand and ungrateful just depressing and foolish. But helping Vietnam is helping SEA and Chinese border. So I am not against donation.