Half a year was simply not enough for Zhao Bolin to create an antidote. Not only did he have to take samples from the zombie itself, but he also had to do clinical trials to ensure that the antidote was ready to be injected into a human's body. The whole process was full of risk and unknown triggers.
It took more than five months for the first formulation to be produced, just a few days short of the deadline given by the government. To test its effectiveness, they caught a few zombies and used them as the experiment objects and to their utter surprise, the antidote worked! The zombie's features gradually disappeared and the person's consciousness slowly surfaced!
The whole team — no, the whole world — cheered, except Zhao Bolin.
Nobody knew how complicated human's genetics was more than him. What were the odds that their first experiment was a huge success? Even if one were to beat him to death, Zhao Bolin still would not believe it.