The subject of the film was protection. Trying to live according to some rules in such a way which protects one’s life from dangers.
The girl leads a really “clean” life. She works in a laundry. She symbolizes well-educated young people. She becomes infected by accident.
The father symbolizes all parents who take care of their children. Additionally he is very strict about leading a healthy life, eating healthy food etc.
The “boy knifer” symbolizes danger you cannot control and which is unpredictable. He is also a symbol of the men who cannot create their own “world” without looking around all the time, their own world which will be the protection from every day cruel life, cruel world.