Doctors recommend that adults and adolescents who will be around infants be vaccinated with a single dose of Tdap. This could include parents, siblings, grandparents, babysitters, and other child care providers. Tdap protects against, among other diseases, pertussis. Infants are too young to be fully immunized against pertussis, but an infant's exposure to the illness can be reduced if he or she only comes into contact with people who are vaccinated. This practice is called cocooning.