i read that people get flu shots annually because flu strains change. do strains of other diseases change?
some viruses tend to adapt and mutate (change) and the influenza virus changes all of the time. medical science has a full time job keeping up with this primitive adaptation. bacteria can change too. this is why we have drug-resistant strains of staph (mrsa). yes you have to get a different flu vaccine every year depending on the strains that are circulating. people who had pertussis (whooping cough) as a child are not always immune for life -- the recent epidemic proves this. be glad that we have scientists keeping track of these things!