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How Does a Mother’s Tdap Shot Protect a Newborn Baby?

We know that pregnant women are supposed to get a Tdap vaccine.

Although recommendations on exactly when to get it have changed over the years, it has been a universal recommendation for pregnant women since at least 2011.

Newborns and infants have the highest rates of death from pertussis.
Newborns and infants have the highest rates of death from pertussis and need extra protection from the Tdap shot that their mother got during her third trimester.

But why?

Mother’s Tdap Shot Protects Her Newborn Baby

It’s about passive immunity.

“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.”

Updated Recommendations for Use of Tetanus Toxoid, Reduced Diphtheria Toxoid, and Acellular Pertussis Vaccine (Tdap) in Pregnant Women — Advisory Committee on Immunization Practices (ACIP), 2012

A dose of Tdap in the third trimester helps ensure that both mother and baby have as much protection against pertussis as possible, as those newly formed antibodies pass to them through the placenta.

“To maximize the maternal antibody response and passive antibody transfer to the infant, optimal timing for Tdap administration is between 27 and 36 weeks gestation although Tdap may be given at any time during pregnancy.”

Updated Recommendations for Use of Tetanus Toxoid, Reduced Diphtheria Toxoid, and Acellular Pertussis Vaccine (Tdap) in Pregnant Women — Advisory Committee on Immunization Practices (ACIP), 2012

But do you really have to wait until the third trimester?

“The mother-to-fetus transfer of IgG may begin as early as 13 weeks of gestation; however, the largest amount of anti-bodies is transferred in the third trimester.”

Plotkin’s Vaccines 7th Edition

You can give the dose earlier if really necessary, but the third trimester is ideal, as it provides maximum protection for the mother around the time of delivery and ensures that the baby gets as many antibodies as possible.

But doesn’t passive immunity from a mother’s previous vaccine doses provide protection to her new baby?

In many cases, yes.

As long as a mother has immunity to a disease, whether from a vaccine or natural infection, she will pass on temporary immunity to that disease to her baby. We see this type of passive immunity for many diseases, including measles, chicken pox, etc.

Unfortunately, waning immunity from pertussis vaccines means that pregnant mothers need a Tdap vaccine with each and every pregnancy to get those antibody levels high enough to protect her baby.

Pertussis is a life-threatening disease for newborns and young infants.

Tdap is a safe vaccine, with few risks.

“Fewer babies will be hospitalized for and die from pertussis when Tdap is given during pregnancy rather than during the postpartum period.”

5 Facts about Tdap and Pregnancy

Get vaccinated and protect yourself and your baby when you are pregnant.

More on Tdap in Pregnancy

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