I'll go into more detail
- The zombies could represent:
- The public baying for blood (literal representation)
- The public becoming obsessed with the housemates and can't stop watching them
- The public attacking the housemates at every opportunity
- The housemates don't want to leave the house- they don't want to become zombies
- The public being uncontrollable and forgetting the housemates are people
- Mob like mentality the public have
Basically if you watch it again and think of the living as the housemates and the public as the zombies it makes a lot more sense