Why does drug resistance easily evolve but vaccine resistance does not?
Very good question and a very good answers in this article!<p>I'll add one more reason not explored by the authors: antibodies don't "leak" in the environment, in contrast to the antibiotics which are everywhere.<p>For example, if I'm vaccinated against <i>S. pneumoniae</i> (one of the bacteria that can cause pneumonia), the bacteria have to get inside my body to gain exposure to my vaccine-induced antibodies. This makes the emergence of resistance very unlikely because :<p>(1) the number of bacteria that are exposed to the antibody is relatively small, because the antibody response is pretty fast and happens before the bacteria had a chance to multiply to significant numbers;
(2) any bacteria clones who evolve resistance to the antibody remain susceptible to the myriad of other immunes peptides, to macrophages, and so on. In other words, as long as I survive my pneumonia, no resistance can ever emerge, because I will kill all the resistant clones through other means.<p>Contrast this to antibiotics. I have pneumonia, I take antibiotics, I'm cured. However, I excrete those antibiotics in urine and stool. Outside of my body, enormous numbers of bacteria are exposed to minute doses of antibiotics. The number of surviving clones is likely to be very high, and those survivors do not face any supplemental threat. Thus, resistance to that antibiotic can be transmitted to later generations.