Re: Past history of illness = immunity?
The problem with flu is that it keeps undergoing genetic recombination and mutations to make new strains of the virus. If you have had one strain, you are immune to that same exact strain but not any others. So no, having the flu doesn't make you immune to it, nor does it make you more susceptible to it than you were before. It can confer a small bit of immunity if the strain you had before is very similar to a current strain, but that depends on how closely related the strains are.