During the 1960s, the USSR was developing a weaponized form of rabies. Essentially, this disease would appear as a normal fever but the victims would eventually turn crazy and start attacking those around them, spreading the illness through bites. If this had been kept secret and the populace were unprepared, the Soviets could have inflicted massive casualties by releasing the weapon in the US using a few sleeper agents. This was designed as part of a strategy to to weaken the US at home should war break out in Europe. This was an ideal solution to the inability of the Soviets (at the time) to strike the US with a crippling nuclear attack. In order to prepare the populace, the CIA covertly funded the production of zombie movies. These were superior, they figured to outright propaganda films, as they were less likely to cause a scare or to upset relations with the USSR. These embedded in the minds of Americans the idea of a plague that rendered its victims beyond control and as such, they had to be eliminated. Think about it: do you know what to do in the event of a zombie plague? Simple: Take a defensive position, arm yourself, isolate the wounded and sick. That's all you'd need to survive an outbreak of weaponized rabies. As the Soviets' abilities to strike the US with nuclear weapons improved, their studies into biological weapons diminished. However, we're still ingrained with that relic of the era in our popular culture.