An one-to-one correspondence between two sets exists only if a mapping exists between the two sets such that each element of the first set maps to exactly one element of the second set and each element of the second set maps to exactly one element of the first set.
Everyone needs protection from tetanus. The DTaP vaccine (diphtheria, tetanus, and pertussis) can help prevent tetanus in young children. DTaP shots are recommended for healthy babies at ages 2, 4, and 6 months, and again at 15 through 18 months. A DTaP booster is recommended for children ages 4 through 6 years old.
Tetanus toxoid (TT), the vaccine that protects mothers and newborns from tetanus, is a detoxified version of the toxin (poison) that causes the disease. A fourth variety of vaccine, such as that for Haemophilus influenzae type b (Hib), uses only the components of the virus or bacteria that provoke an immune response.