Study Finds Third Trimester Vaccine Significantly Reduces Pertussis In Infants

Jun 15, 2018

Brenda Reyes receives a Tdap vaccination during her third trimester at UNC Chapel Hill's Aycock Family Medicine Center.
Credit James Morrison / WUNC

A study published in the American Journal of Preventive Medicine Friday finds that infants whose mothers get a Tetanus, Diphtheria, Acellular Pertussis -or ‘Tdap’- vaccine during the third trimester of pregnancy are significantly less likely to get pertussis.

UNC Chapel Hill researcher Dr. Sylvia Becker-Dreps is lead author of the study. She analyzed more than 675,000 insurance claims to compare the rates of pertussis in infants whose mothers received a Tdap vaccine and those whose mothers didn’t.

“What we found is that in the first six months of life, infants whose mothers were vaccinated had 75 percent less hospitalizations for pertussis as compared to moms who did not get the vaccine,” Becker-Dreps said.

Overall, the study found infants whose mothers received a prenatal Tdap immunization were half as likely to get pertussis as those whose mothers forewent the vaccine.  

Since 2011, the CDC has recommended women receive a Tdap vaccine during the third trimester of pregnancy as a way to pass on immunity to their child. Pertussis, also known as whooping cough, is a highly contagious respiratory disease. It can be deadly in infants who are especially vulnerable until they receive their third Tdap shot 6 months after birth.

This study further supports the CDC recommendation by finding that reductions in pertussis only occur when the prenatal Tdap vaccine is administered after 27 weeks of pregnancy.  

“What we think is happening is if you get it late in pregnancy you have the strongest immune response closest to delivery so you’re giving the highest level of antibodies to the baby,” Becker-Dreps said.

Most women who get the vaccine do so in the third trimester. But only about half of all pregnant women are getting the Tdap vaccine. Some pregnant women are forgoing immunization based on unsupported claims that vaccines can lead to autism in children.


Becker-Dreps understands that fear, but recommends pregnant women get a prenatal Tdap.


“Our study shows you can actually cause harm by not getting the vaccine,” Becker-Dreps said. “Because it’s so effective at preventing pertussis.”