Body & HealthFact
Your body has antibodies for pathogens that don't exist yet.
Your genome holds only about 20,000 genes, yet your immune system can produce more than 10 billion different antibodies. The trick is called V(D)J recombination: each developing B cell shuffles its own combination from some 150 gene segments and adds random cuts at the joints. The result is a repertoire that recognises even completely new pathogens.
Useful: That is why a defence against a new virus already exists and only needs to be multiplied.
Source: en.wikipedia.org