Though warned of how deadly these infected animals are, the animalists allow one chimp to escape its cage, thus unleashing a worldwide pandemic that takes a mere 28 days to cover the globe. There's something interesting here about how it is easy to ignore something important if that something doesn't fit our preconceived ideas. The attendant at the lab is deemed irrelevant -- is it because he is seen to be a mere cipher in a system or because he is the enemy.
A related reduction of reason occurs with the survivors a British army unit. The commanding officer is a man of apparent civility: he maintains that hot water is a benchmark of civilization; he wants to understand how to defeat the virus and survive the infected. Yet when one soldier in his unit becomes infected he chains him up to "study" how the infected survive and how long it will take them to starve.
In a certain way the film comes full circle at this point. Private Mailer is treated in the same way those chimps were: something to be examined for the greater good.
Along with the negative example of how humanity is diminished when we are careless, there is the fascinating question of what makes life worth living or if simple survival is enough in a world gone literally to hell.
After waking up from a serious accident, Jim (played by Cillian Murphy) wanders around a deserted London trying to figure out what has happened. He is rescued from some of the infected by Mark (Noah Hurtley) and Selena (Naomie Harris). After Mark becomes infected, Selena has the foresight to kill him; she tells Jim that the only thing that matters is survival. Jim strongly disagrees. But it is not theory or rhetoric that changes her mind:
Jim: Do you know I was thinking?
Selena: You were thinking that you'll never hear another piece of original music ever again. You'll never read a book that hasn't already been written or see a film that hasn't already been shot.
Jim: Um, that's what you were thinking.
Selena: No. I was thinking I was wrong.
Jim: About what?
Selena: All the death. All the shit. It doesn't really mean anything to Frank and Hannah because... Well, she's got a Dad and he's got his daughter. So, I was wrong when I said that staying alive is as good as it gets.
Jim: See, that's what I was thinking.