Sony Reader, and since the digital form of manga distribution is still in its infancy, it can take a will while for the digital version to catch up with the print version. Only the first 5 volumes of I Am A Hero are available online, so when I found myself stuck at the station the other day, I picked up volume 6 in paperback.
We often see with zombie series that continue long enough, that there is some evolution, whether it's George A Romero's zombies slowly developing and regaining some cognitive abilities, the 28 Days/Weeks later series where we see carriers of the Rage virus who don't turn.
The zombies in I Am A Hero are more the fast 28 Days Later, super aggressive zombies. I hope this is not too much of a plot spoiler, but after one of the main characters, Hiromi Hayakari is bitten by a zombie baby, she has some immunity to the virus and although she develops a speech and physical disability, she lacks the classic zombie brain crazing. This gives the group hope that infection is not a death sentence, and a cure is possible. I'm very interested to see how the story develops now that keeping Hiromi alive is one of the central story threads.
Kengo Hanazawa on Twitter: https://twitter.com/hanamanko
I Am A Hero website: http://spi-net.jp/rensai_sakuhin/i_am_a_hero/index.html