The routine use of pertussis booster vaccines in the adolescent and adult population reduces disease morbidity and provides protection of unvaccinated or incompletely vaccinated infants via herd immunity. An enhanced pertussis surveillance study conducted between 1999 and 2002 found that among 264 infant pertussis infections, when a source could be identified, one third were infected from their mother, 15% from their father, and 20% from an older sibling.2 A study of risk factors for pertussis related hospitalizations in infants found that siblings were the most common route of infection (53%), followed by parents (20%), other relatives (12%), neighbors (8%), and day care contacts (3%).3 Clearly, infants are infected by the people around them, especially those with the closest contact.

While a single booster Tdap dose is recommended for all adolescents and adults, additional booster doses were added as an ACIP recommendation to be given to all women during each pregnancy. The rationale for doing so is two fold. First, the vaccine booster will reduce the possibility that the mother will develop a pertussis infection while the infant is young. Second, the booster dose of Tdap during pregnancy allows the opportunity for transplacental anti-pertussis antibodies to offer passive protection to the newborn infant for the first few months of life when the infant is still too young to start the primary DTaP vaccine series. While this passive form of protection is expected to wane in the first months of life, it is important to note that most pertussis deaths occur prior to age three months so providing Tdap boosters to all pregnant women could reduce pertussis infant mortality. In one study, more than 90% of surveyed obstetricians were aware of the ACIP recommendation to immunize their patients during pregnancy, but only 67% had the vaccine available in their office.4

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