Answer:
Viruses could have a high mutation rate
Explanation:
Viruses replicate very fast when they enter into the bloodstream. This isn’t however the real cause of why a secondary immune system isn’t possible against them.
The main cause is because they mutate rapidly. The immune system already has an idea of the genetic composition of the pathogen exposed to previously and knows how to fight it. But the viruses undergoes some genetic alterations which then makes it hard for the secondary immune response to attack and kill them.
