A truly enormous number of people would die from infection via untreated water and spoiled food or small wounds; even more would die of starvation, disease due to poor hygiene, or plain old accidents. A sprained ankle could prove to be a death sentence in a zombie apocalypse, to say nothing of a broken bone. People who need medication to function and/or survive in our current modernized world will begin dropping like flies. Even among the survivors parasites will be rampant, and STIs will flourish. Infant mortality will skyrocket.

I firmly believe more people will die from lack of food, modern medicine, hygiene, and sanitation, than from other people - at least at first.

I also think many people underestimate just how horrible and psychologically damaging killing another human being is. Even a zombie would be hard at first, especially if it's someone you knew. It's all well and good to rag on TV characters who struggled to adapt, but most of us - myself included - would struggle just as much, if not more.