When my children were small they were vaccinated against various
ailments, polio, smallpox, diphtheria, whooping cough etc.   In some
cases only one treatment was required in others a booster was required
shortly after but in either case the jab was effect for life,
hopefully three score and ten.

Why then does my dog needs a booster every twelve months?  Surely a
dog's immune system is no less efficient than mine?
-- 
Alex