evidence: All adults should receive one dose of Tdap vaccine if they have not previously received pertussis-containing vaccines in adulthood. In particular, adults who have not previously received pertussis-containing vaccines in adulthood, and who anticipate having regular contact with an infant, should receive a dose of Tdap vaccine, ideally administered at least 2 weeks before contact with the infant. Persons who have had pertussis infection should receive pertussis-containing vaccines as recommended because infection does not confer long term immunity. A Tdap vaccine should be routinely offered to all pregnant women in every pregnancy, irrespective of their immunization history. One dose of Tdap vaccine should ideally be provided between 27 and 32 weeks of gestation. Earlier immunization between 13 and 26 weeks of gestation may also be considered in some situations (e.g. in case of an increased risk of preterm delivery or travel) to allow for longer placental exposure to higher antibody levels and maximization of antibody transfer. While it is preferable that immunization is administered at least 4 weeks before birth to allow optimal transfer of antibodies and direct protection of the infant against pertussis, it should be considered until the end of pregnancy as it has the potential to provide partial protection. [...] All health care and child care workers, regardless of age, should receive a single dose of Tdap vaccine for pertussis protection if this vaccine was not previously administered in adulthood, even if the person is not due for a tetanus and diphtheria booster. Refer to Immunization of Workers in Part 3 for additional general information.