in a former thread on the issue of deadly flu epidemics why do flu epidemics, like 1918 one, end? - Factual Questions - Straight Dope Message Board it has been said that such epidemics eventually end because of the natural process of appearance of benign strains that confer immunity
[QUOTE=Blake]
So while the original strain virus remains infective for a few weeks, and can only readily infect those nursing the sick for most f that time, the less lethal form can potentially remain infective for months, and during that time can be passed to multiple strangers. As a result the mutant strain infects orders of magnitude more people.
However the two strains are still very closely related, and once a person has fought of one strain they are immune to the other. Because far more people are infected by the mutant strain, the original lethal strain is rapidly outcompeted, and eventually becomes extinct.
[/QUOTE]
Well, so if this happens via natural process, why can’t we do this artificially for any specific deadly flu strain we are dealing with? Are some strains naturally or artificially so made that it is hard to make a harmless strain out of them?