Quite a fun idea and a nice execution. It got me hooked on enough to play a couple of times!
It would be nice to have some high score to try to beat. Also, the powerups were useless to me because I found myself in scenarios where I would have to go through a sea of infected people just to get to safety for a couple of seconds. Maybe make it so that you can pick an item up and use it whenever you see fit?
Overall, a nice experience - good job! :)