There are multiple reasons someone may develop anorexia. Sometimes it is because of stress or anxiety. Most commonly, it is the constant need to feel as if they weight too much and need to remain slim.
Masculinity is often associated with maturity and superiority. To be the only one in a group would make one feel alone and vulnerable and being the last in a group would make one feel inferior. I could give a much more detailed answer but I think it's a simple enough answer to understand without drawn out facts.
Answer:
Previous anaphylaxis reaction to a previously administered vaccine
Current illness
Immune deficiency
