How do scientists know how to make a flu vaccine if viruses can be different every year?

Question: How do scientists know how to make a flu vaccine if viruses can be different every year?

Asked by mollie to Michael on 18 Jun 2010 in Categories: Scientist.
- Michael Loughlin answered on 18 Jun 2010:
  
  well by looking at the current virus a vaccine can be made to that and help fight that flu. And viruses take longer than that to change structure completely
  
  also we are looking at making a vaccine based on aprt of the virus that cannot change or else the virus would fall apart. That would be a vaccine for all flu’s as they all have this same structure

Question: How do scientists know how to make a flu vaccine if viruses can be different every year?