(I'm purposefully ignoring some of the previous chapters)
Jack had to be careful because he didn't want to catch the virus he unleashed on the world. At the same time he didn't want it to be noticeable that he was the only one not getting the virus. He planned it out and then made his wish:
"I wish there was a virus that was airborne and highly contagious but that only one percent of the population would develop symptoms (That way millions would catch the virus before anyone noticed a problem). Only men would show symptoms and the men with the most testosterone would develop the symptoms faster and more severely than the average male. The first stage of infection would last a year without any symptoms. In the second stage, the men would start to lose fat and gain muscle. They would not become massive but they would become fit and athletic and with that would be a mental change, a desire to play sports. In the third stage, they will develop an allergic reaction to all forms of cloth whether natural or synthetic. They will find it difficult to wear clothing. Then in the final stage, they will turn into stone statues. This will be a very gradual transformation the more like a statue they become, the greater will be their desire to become a statue and they will seek drastic measures to remove all blemishes so they can become beautiful statues."
Jack also wished that this virus has already been spreading for a year so that he could witness when people first begin to show symtoms.