Pertussis Vaccine in Pregnancy Key to Preventing Disease in Infants
May 14, 2015

Pregnant women should be vaccinated against pertussis during each pregnancy to best protect babies from infection.

The Global Pertussis Initiative (GPI), an expert scientific forum charged with addressing the global burden of pertussis, announced this recommendation earlier this week.  However, this isn’t the first time we’ve heard this suggestion.  The CDC’s Advisory Committee on Immunization Practices (ACIP) first recommended that women get a Tdap vaccine during pregnancy in October of 2011.  Then, in October of 2012, they updated the recommendation stating that women should get a Tdap vaccine during each pregnancy.

As the GPI decision explained in a recent Medscape article,

Vaccination of women with Tdap during pregnancy is expected to provide some protection to infants from pertussis until they are old enough to be vaccinated themselves. Tdap given to pregnant women will stimulate the development of maternal antipertussis antibodies, which will pass through the placenta, likely providing the newborn with protection against pertussis in early life, and will protect the mother from pertussis around the time of delivery, making her less likely to become infected and transmit pertussis to her infant.   

While this excerpt may suggest the basis behind the GPI’s recommendation, the ACIP’s decision was further referenced in a Morbidity and Mortality Weekly Report (MMWR) published in February, 2012, which explained,

Very young infants are dependent solely on maternal antibodies and lack the ability to mount a cell-mediated response. The effectiveness and optimal concentration of maternal antipertussis antibodies in newborns are not yet known, but high levels of antibodies in the first weeks after birth likely confer protection and might prevent pertussis or modify disease severity. Studies on the persistence of antipertussis antibodies following a dose of Tdap show antibody levels in healthy, nonpregnant adults peak during the first month after vaccination, with substantial antibody decay after 1 year. Antibody kinetics in pregnant women likely would be similar. One study evaluated persistence of maternal antipertussis antibody concentrations from maternal delivery and cord blood pairs from women who received Tdap within the prior 2 years. The estimated antipertussis antibody concentrations at birth in most of these infants were considered unlikely to provide adequate protection. These findings indicate that maternal antibodies from women immunized before pregnancy waned quickly and the concentration of maternal antibodies was unlikely to be high enough to provide passive protection to infants. Because antibody levels wane substantially during the first year after vaccination, ACIP concluded a single dose of Tdap at one pregnancy would be insufficient to provide protection for subsequent pregnancies.

The ACIP went one step further and even suggested that the vaccination of pregnant women preferably occur within the third trimester, stating the following in the MMWR,

Tdap may be administered any time during pregnancy, but vaccination during the third trimester would provide the highest concentration of maternal antibodies to be transferred closer to birth. After receipt of Tdap, a minimum of 2 weeks is required to mount a maximal immune response to the vaccine antigens. Active transport of maternal immunoglobulin G does not substantially take place before 30 weeks of gestation. One study of pregnant women who received Tdap within the prior 2 years noted that maternal antibodies waned quickly; even women immunized during the first or second trimester had low levels of antibodies at term. Therefore, to optimize the concentration of vaccine-specific antipertussis antibodies transported from mother to infant, ACIP concluded that pregnant women should be vaccinated with Tdap during the third trimester.

The CDC offers an extensive list of studies on this subject.  

As we can see with the GPI’s recommendations, experts agree that the primary strategy to protect infants from pertussis is vaccination in pregnancy. While the passive transfer of pertussis antibodies from the mother to the fetus is the best chance at protection, the most robust strategy would be to also immunize family members and other close contacts and caregivers in a secondary line of defense known as “cocooning”.  This is especially helpful in reducing the likelihood of a baby being exposed to pertussis before they can begin their own infant series of pertussis vaccination (DTaP).

According to a new Pediatrics study out this week, the first dose of pertussis vaccine (DTaP) is also protective against severe pneumonia, hospitalization and death. This is especially important for parents living in areas where there are high numbers of pertussis cases, such as we’ve seen in the state of Washington in 2015.  Since the first dose of DTaP can be administered between 6-8 weeks of age, expectant parents should consider talking to their doctor about the possibility of getting their child the DTaP vaccine at six weeks to help boost their protection as early as possible.

If you know of a family that is expecting, please consider sharing these important recommendations with them.  You could actually help save a child’s life and put a parent’s mind at ease.  

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