The old man nodded grimly. "We have a few people who have been bitten. They're...different. Not quite zombies, but not quite human either."
I frowned. "What do you mean?"
I hesitated. "I'm not sure. I've only been able to test it on people who haven't been bitten yet."
I shook my head. "I don't know. I need to study this... see if I can come up with something."
The survivors nodded, looking resigned. I knew I had to do something, but I was running out of options. The vaccine was not a magic bullet, and I was starting to realize just how limited it was.
"Hey, you're the vaccine guy, right?" one of them asked.
The survivor, a grizzled old man, eyed me warily. "We've heard of your vaccine. It works, but it's not a cure-all. What about the people who are already infected?"