I got the "Super survivor" achievement which requirement says "Make it through the 2010 infection without being infected!"
I'd still like to try for the zombie achievements but does this mean it's too late for me to become infected?
No, you can still become infected. Someone has a board in the bragging forum, about recently just getting infected.
I know of a few people who have been infected since they got the achievement, so I'd say keep trying and you should get infected eventually!