Tdap is the abbreviated name for the tetanus-diptheria-acellular-pertussis vaccination. Guidelines for the vaccination of pregnant women have changed on the heels of the 2012 Tdap outbreak that included nearly 100% of the US states and Washington, DC. ACIP, the Advisory Committee on Immunization Practices, updated the information found on the Centers for Disease Control and Prevention website as of February 2013.

According to old Tdap guidelines, a Tdap vaccination was suggested after the 20th week of pregnancy or after baby was born. Newborns are too young to be vaccinated at birth, but they are the most susceptible to Tdap infection. Infants accounted for the majority of pertussis deaths in 2012, so ACIP changed the vaccination policy to increase maternal and infant immunity.

The New Tdap guidelines suggest immunization between 27 and 36 weeks of pregnancy even if the pregnant woman has been immunized in the past. Tdap levels peak at one month making this the perfect time to boost maternal antibody levels. Doctors are also encouraged to revaccinate women during every subsequent pregnancy as antibodies start to decline one year after vaccination.

ACIP recognizes the fact that the Food and Drug Administration (FDA) approves Tdap immunizations as a one-time adult vaccination, but off-label use to boost maternal antibodies and protect against infant infection is backed with sound research.

ACIP suggested future studies be conducted on the risk of serious adverse side effects in women vaccinated during subsequent pregnancies. There is also little information on possible side effects when pregnancies are spaced close together. ACIP plans to follow reported adverse side effects using VAERS – the Vaccine Adverse Event Reporting System and VSD – the Vaccine Safety Datalink. Several years of data collection will be required to establish a conclusive report on adverse side effects with multiple Tdap vaccinations during pregnancy.

It takes two weeks for Tdap to mount antibodies in the human body. Peak levels are measured at one-month post vaccination. For this reason, ACIP suggests vaccination during pregnancy between the 27th and 36th week. There is no mention of altering the vaccination time period in special situations, such as pregnancy with multiples, when a full-term delivery may not be viable. The Tdap vaccination can be administered at any time during pregnancy, so obstetricians have the final call in terms of vaccination timing if early delivery is suspected.

Sources: Medscape News Today, CDC: Updated Vaccination Guidelines for Tdap