A vaccine does teach your immune system how to fight a disease - a vaccine works by introducing your immune system to a fragment of a virus so that it develops the means to identify and destroy that fragment, giving it a head start to do the same thing to the same portion of the virus if it ever encounters the unadulterated whole.
And vaccination does not cause increased lethality of viruses. Preparing your immune system to kill an infection before it has time to replicate makes it less likely for a more dangerous mutation to emerge, because there is less opportunity for an advantageous defect to arise if the infection reproduces less before your immune system wipes it out.
No, you don't understand vaccines.
A vaccine does teach your immune system how to fight a disease - a vaccine works by introducing your immune system to a fragment of a virus so that it develops the means to identify and destroy that fragment, giving it a head start to do the same thing to the same portion of the virus if it ever encounters the unadulterated whole.
And vaccination does not cause increased lethality of viruses. Preparing your immune system to kill an infection before it has time to replicate makes it less likely for a more dangerous mutation to emerge, because there is less opportunity for an advantageous defect to arise if the infection reproduces less before your immune system wipes it out.