A secondary immune response occurs when an antigen is encountered on a second occasion, due to exposure to a pathogen that previously caused infection. Which property of some viruses explains the lack of a secondary immune response

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.

Answer: The ability of virus to undergo rapid mutation.

Explanation: Secondary immune response is initiated when a particular antigen attack the same host again. In secondary immune response organism attacked has previous knowledge of the virus and how to work against the virus but when virus mutates, that is, change in genetic makeup, the organism will not show secondary immune response since there is change already and the previous knowledge about the virus is no longer applicable. Also this doesn't make the organism not to have secondary immune response but the rapid virus mutation discard secondary immune response system.