How come some humans are more vulnerable to illness than others? Do some humans just have worse luck, or is it

Question: How come some humans are more vulnerable to illness than others? Do some humans just have worse luck, or is it something wrong with their body?
- Keywords:
  disease,
  human,
  virus
Asked by to Daren on 17 Jun 2014. This question was also asked by .
- Daren Fearon answered on 17 Jun 2014:
  
  Excellent question.
  
  Some people are born with what is called a genetic predisposition to certain diseases. This means that they have a greater chance of developing a particular disease such as cancer or alzheimer’s disease. There is a lot of work going on into better ways of identifying people with these genes so that we can help them avoid the disease. This also works the opposite way and some people have developed resistance to viruses such as HIV.
  
  Another factor depends on your environment. Your immune system can be very good at fighting off disease and infections. Usually if you have become sick your immune system will remember what caused it and develop things called antibodies which will help recognise the cause of the disease in the future so you can fight it off faster! People with stronger immune systems tend to get sick less.

Question: How come some humans are more vulnerable to illness than others? Do some humans just have worse luck, or is it something wrong with their body?