There is no more chaos because almost all un-infected people are either dead or in another country. The infection neeRAB feeding and by all accounts infected meat cannot be eaten by the infected. As with most predators, if there isn't a sufficient source of food then the best thing to do is conserve your energy. If you thinks about it, it is very unlikely that people would get infected whilst driving, thats probably why there were not alot of burning or piled up car wrecks.
Thats the point, it doesn't make you attack everything that moves. They are not just attacking for the sake of attacking, they are attacking for food. As I said before, it looks like the infected cant eat infected meat.
How would a country function when its population consists of bloodthirsty beasts that are intent of feeding off every living thing on the island? Again, how would the government be able to function if every member of the cabinet was reduced to a rabid animal. Once all food sources had dried up, then surely everyone would die?
It's a case of getting to these places though, if you think about it petrol would be in short supply, as with every epidemic resources would run low, the supply chain would break down, there would eventually be no workers to maintain a supply chain of resources such as petrol or electricity. How are you going to get to these places without petrol? As for hiding in London, this place would be infested with infected people, it would be a game of cat and mouse.
Why would there need to be tight security at a lab that was researcing viruses? The scientists were researcing a new virus that was found in some monkeys, not knowing what the implications could have been if this virus escaped. Why would you need alot a security for a bunch of monkeys with a virus that was not really known about?
This film did maintain controls and boundries whilst extenting the realms of reality, everything in this film was relevant and everything tied in with the plot. The thing is alot of the stuff was not explain to you, unlike genres like star trek where everything is explained. But if you put some thought into it and realised the implications of such a epidemic, you would see this could be quite true.
But, like most peole have said, the film did turn into a pile of tosh as soon as they met up with the soldiers.