It's a very smartly written novel that holds up very well. It's also unusually grim for the era.

Steven Soderbergh's Contagion also comes to mind as an example of a realistic, scientifically accurate depiction of an epidemic.

Michael Crichton's The Andromeda Strain, while not being about zombies, is a very science/fact-based exploration of a hypothetical outbreak. A much less scary scenario, though; the pathogen only affects a single, isolated town which is quickly secured, and all of the action occurs in the experimental underground science lab where they study it. The 1971 film is also fantastic, and holds up really well.