This pregnant patient should receive the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine now. To decrease the burden of pertussis in infants (who are at the greatest risk for the disease), the Advisory Committee on Immunization Practices (ACIP) recommends that pregnant women receive a single dose of the Tdap vaccine during each pregnancy, regardless of when they last received either the tetanus and diphtheria (Td) or Tdap vaccine. Because maternal immunity wanes over time, administering the Tdap vaccine between 27 and 36 weeks' gestation is thought to provide optimal protection against pertussis for the infant throughout the newborn period, during which time the child is solely dependent upon maternal antibodies for protection, by boosting the mother's antibody levels. The Td and Tdap vaccines do not contain live elements and are considered safe to administer to pregnant women, as there is no evidence to suggest an increased rate of adverse events in this population.

Although the Tdap vaccine can be given at any point during a woman's pregnancy, administering the vaccine between 27 and 36 weeks' gestation is thought to confer maximal antibody protection to newborn infants. It is not advisable to wait until after 36 weeks of pregnancy.

The Td vaccine does not provide protection against pertussis and therefore should not be given either now or after 36 weeks' gestation.

Withholding vaccination against tetanus, diphtheria, and acellular pertussis during pregnancy is inappropriate. Although this patient received the Tdap vaccine during her first pregnancy, that vaccination is unlikely to provide sufficient protection for her second child at the time of delivery, as antibody levels wane significantly during the first year after vaccination.