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.
Booster vaccines needed to keep up protection from tetanus. The DTaP does not offer lifetime protection. People need booster vaccines to keep up protection from tetanus. Children should get a booster vaccine called Tdap (which protects against tetanus, diphtheria, and whooping cough) at 11 or 12 years of age. Adults need a booster called the Td vaccine (for tetanus and diphtheria) every 10 years. Adults should also receive a one-time shot of the Tdap vaccine in place of one Td shot.