I enjoy zombie settings, however I'm usually unsatisfied with their being magical - being able to be "alive" while dead, and so on. So I've been giving thought to something a bit more realistic - not realistic, but closer to that end than what is essentially a modern fantasy setting like The Walking Dead.

In the early 21st century a new rabies variant pneumonic lyssavirus emerged from a lab somewhere in North America, derived from a bear variant of the virus. It was originally designed as a "humane" bioweapon, designed to create fear in the target population, but kill only a small number of them. This strain is far more deadly and unpredictable than previous versions, with an incubation period of 2-12 weeks. Initial symptoms resemble influenza or tuberculosis, including high fever, severe cough, chest pain, and fatigue, often leading to difficulty breathing.
 
A fraction of infected inviduals die immediately within hours of the onset of symptoms due to overwhelming systemic shock.
 
Most succumb more slowly over several days or at most weeks as the virus ravages their nervous system and vital organs, causing violent seizures and eventually fatal brain damage.

A minority survives but experiences irreversible aggression, paranoia, violent tendencies, and significant memory loss, making them a danger to others even post-recovery. They also develop an unusual requirement for protein, becoming essentially carnivorous and cannibalistic, yet instinctively avoid consuming other infected individuals.
 
Survivors develop a fear of clear water, though seem unperturbed by blood and mud, and will consume vegetable matter for its fluids. They are usually seen to be frothing at the mouth. Over time, these survivors lose vision clarity, their eyes clouding over in glaucoma (many have developed type II diabetes mellitus as a result of their diet) but develop stronger senses of hearing and smell. As winter approaches they seek to fatten up and hibernate.
 
The virus may be transmitted by the bodily fluids (spit, blood, mucus etc) of a symptomatic individual, even post-mortem.
 
Notably, children appear to be immune to this strain.

Over the years, different kinds of aggressive infected will appear, their behaviour evolving to suit their environment. Some will remain solitary, some will hunt in packs and protect their young (who remain uninfected, but their upbringing will be somewhat deficient). Some will avoid the day and prefer to hunt at night where they have an advantage. Some will take to make clicking and whistling noises to communicate and use echolocation to hunt. Some will hide in buildings, others in forests. They'll tend to do better in tropical areas with lots of wildlife than in colder areas with less.