February 12, 2015

VU study explores optimal timing for pertussis vaccine

Pertussis, commonly known as whooping cough, is experiencing a resurgence, and its tiniest victims are not armed to battle the contagious respiratory infection.

Pertussis, commonly known as whooping cough, is experiencing a resurgence, and its tiniest victims are not armed to battle the contagious respiratory infection.

Kim Fortner, M.D., assistant professor of Obstetrics and Gynecology at Vanderbilt University Medical Center, and her colleagues in the Vanderbilt Vaccine Research Program want to change that.

Amy Darrow receives a Tdap vaccination for pertussis from Amber Thompson, LPN, as part of a Vanderbilt clinical trial.

The group recently embarked on a study funded by the Centers for Disease Control and Prevention to test the tolerance of repeated dosing with the Tdap vaccination during pregnancy in hopes that the overall benefit provides protection to newborns.

The idea is that transplacental passage of antibodies will provide coverage for both the mother and the baby, which Fortner sees as a win-win situation.

“There is dual benefit when the mom manufactures antibodies and is transporting them across the placenta,” Fortner said. “In essence, you are using the mom as an antibody manufacturing mechanism. And she is able to provide some protection for her baby.

“Cases of whooping cough are on the rise. Newborn immunization was not effective, so there is no way to protect the newborn in any way and they don’t fare well when they get the disease. They have a much higher mortality rate.”

Fortner recalled the story of one of her patients who had an uncomplicated pregnancy. After delivering her daughter at 34 weeks the baby spent two weeks in the NICU. When she was 36 days old she developed a cough. Two days later the family returned to the pediatrician. Their baby died after going into respiratory arrest from pertussis infection.

“I can still hear her saying ‘Nobody mentioned it…Nobody brought it up. Nobody talked about it. I would have gotten the vaccine,” said Fortner. “This was before 2008 when the recommendation from the Advisory Committee on Immunization Practices (ACIP) was to provide the vaccination postpartum.”

The group of medical and public health experts amended the guidelines in 2011 to offer the vaccination as a prenatal dose. Data from the current study will be used to determine if further changes to the guidelines are necessary.

As the primary site, Vanderbilt is halfway to meeting its enrollment requirement of 250 pregnant women to investigate the safety of repeated doses of Tdap.

Study participants receive standard/routine prenatal care in addition to allowing for an additional blood draw prior to the Tdap vaccination and one month following. The women are also asked to record any symptoms during the first seven days after receiving the vaccination. Mothers and babies will be followed for six months post delivery.

DTap vaccination guidelines for children call for a total of five doses — at 2 months old, 4 months old, 6 months old, between 12-18 months old and between 4-6 years old.

Currently Tdap is recommended for all pregnant women between 20-34 weeks gestation based on data that antibodies begin to cross the placenta around 18 weeks with peak times during 30-32 weeks of gestation.

As the study reaches its goal for pregnant participants, Fortner has begun the second phase of recruitment for non-pregnant women to compare the antibody responses.

In addition to evaluating maternal tolerance to the Tdap vaccine, the study is also comparing immune response by way of antibody levels between pregnant and nonpregnant women.

“We know the vaccine is safe to give during pregnancy,” said Fortner. “The question we want to answer: ‘Is there a more optimal schedule for giving the vaccine to ensure the best maternal outcome and to best protect the newborn?’ There is no doubt that vaccination remains the single most effective strategy for prevention and infection.

“But like so many things, it is such an important question. We can’t go back and try to protect the newborn. You have to do it before you know you need it.”

Interested study participants can call 615-322-2730 or go to vaccineresearch@vander-bilt.edu.