It is assumed that mothers immunized for pertussis (Tdap) pass enough antibodies on to the infant to protect against infection until infant Tdap immunizations begin, but researchers at Texas Children's Hospital recently concluded a study comprised of 105 pregnant women to measure the exact amount of antibodies passed on to infants. If antibodies are not passed in sufficient amounts the infant is not protected until vaccination begins.

The 105 participants ranged in age from 15.3 to 38.4 with an average age of 25 years. All participants were at least 37 weeks pregnant and had received a Tdap booster immunization within the last 24 months. Maternal and cord blood tests were used to measure serum quantities of pertussis antibodies. Researchers found no difference between cord blood and maternal measurements when Tdap boosters were given before pregnancy or in the early stages of pregnancy. At two months, infant antibodies were present in sufficient quantities to protect against infection. Researchers note individual cases may exist that require late pregnancy vaccination or re-immunization between pregnancies to maintain protective levels of pertussis antibodies.

Source: Healy CM, Rench MA, Baker CJ. Importance of Timing of Maternal Tdap Immunization and Protection of Young Infants. Clin Infect Dis. 2012 Oct 26.

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