In 28 weeks later, the military initiates Code Red when the virus breaks out, and the soldiers were order to kill everyone, even those who were healthy.
What’s the point of it though?
It made for an impressive shootout for sure, but it isn’t very effective. The infected turn into zombies pretty much instantly, so it’s not possible for the infected to hide their infection.
Was it somehow explained in the movie, or is just a plot convenience to give us a cool scene?