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.
Adults who have sustained injuries deemed to be tetanus-prone (all wounds other than clean minor cuts) should receive a booster dose of dT if more than 5 years have elapsed since the last dose of tetanus-containing vaccine (refer to Table 4.19.1).