Ever since the zombie virus broke out from Lab 51 District, the Hong Kong government responded by setting up a 5-kilometer blockade around the perimeter of the outbreak. No one could get in. People living in 51 District could only rely on themselves to run away and stay alive. Some even gave up the battle in the end.
On grounds of public safety, isolation of affected areas was the usual and only thing the government was capable of. Hence, many civil combat groups have emerged around the world, fighting the battle on a mission to restore humanity themselves. Amongst them was ZST, an American organization who aims to save the needy, eliminate the evil, and rebuild homes.
ZST heard from Marian about the outbreak in Hong Kong Island's 51 District, which was to them an important battlefield. They agreed to send Jack Lee, their best combatant in their squad, and weapons expert Ethan to Hong Kong to carry out this rescue mission.
After the outbreak, Dr. Banner was in such a rush to develop a vaccine that he injected the serum and virus in his own body. After a while, he too turned into a zombie with a bit of human left in him. He disappeared.
The zombies from the lab reached ground level, attacking human beings and occupying nearby buildings.