Subject: Would it ever be necessary to find the 'patient zero' of a virus?

I'm writing a story and would love to know if there would ever be a case where 
it was necessary to find the first person infected by a particular virus (i.e. 
because the virus had mutated at an unusually high rate and the only way to 
develop a vaccine was to find it's core structure - the point of origin for 
all of the various mutations.)

Re: Would it ever be necessary to find the 'patient zero' of a virus?