Question

Why it is difficult to make vaccines for viral diseases?

Answer 1

It is difficult to make vaccines for viral  diseases since virus use the machinery of our body thus making the vaccination difficult.

Answer 2

Virus does not show any feature that living organisms have. But the begin to show signs of life only when they enter the body of a living organism and starts to use its machinary for living.

So, as they don’t show life outside, we cannot culture them and so we cannot make vaccines for viral diseases.