In "28 Days" we have a violation of containment protocol by someone who was not authorized, then the idiot proceeds to kiss his wife despite being infected. And his ability to escape undetected and then squirm his way back into the public to cause mass infection all over again... not very believable.
There is some possibility of widespread contamination happening, but... the movies do take liberties with punching holes through defenses we are heavily relying upon in reality, to upset and instill fear in us. That's the entertainment.
In reality, if a virus outbreak occurs we have a major lock-down take place. Look at what happened in Boston after the marathon massacre, and that's just to avoid a nut job.
I think our societies would be pretty adept at providing isolation of an infectious disease (as in the 1990's movie "Outbreak
"). Of course, Soderbergh took a more nasty turn with it in Contagion
, but I found it less believable. However, there are scenarios where many hundred thousands or millions may die. Some fanatical imbecile believing he is doing what God wants is going to infect a massive water supply somewhere in the USA at some point in the future. And it won't be detected until many people are sick and spreading it. Just look at what happened the other day
, about some Middle Eastern foreigners steeped in chemical engineering knowledge milling about at night around a Boston area water supply. Given the ease of their break in, I fear this was a test and will pave the way for something lethal sometime soon.
On a larger scale, what we REALLY have to worry about is a collapse of the agricultural machine. The ecosystem is becoming more vulnerable. If colony collapse disorder continues at the rate it is going, we won't have any bees left and more than 40% of the crops we subsist on won't be pollinated, failing to reproduce. So we have an enlarging population with a shrinking food supply. That's the more plausible scenario of mass chaos and death.