Question

Why does not the vaccine works all the time?

Answer 1

Answer:

Vaccines are among the most ingenious of inventions, and among the most maddening.

Some global killers, like smallpox and polio, have been totally or nearly eradicated by products made with methods dating back to Louis Pasteur. Others, like malaria and H.I.V., utterly frustrate scientists to this day, despite astonishing new weapons like gene-editing.