By kissing a lot?
You could become infected by wearing one of the zombie masks and refreshing on the Shadowglen Graveyard page. Unfortunately, you're a day late - as of yesterday, you can't get infected anymore.
Was there an announcement?
I was also a day late. They could of given us a headsup when the event was over in plain sight. I'm a newbie I didn't even know where and how to get infected. Not cool =/
Sh*t! I was gone for a week on holiday, and I didn't even have a chance to get infected! Unfair! D';
HAVE A NICE DAY ! <3