Immunizing pregnant women with Tdap protects newborn infants against pertussis, but a study published in Clinical Infectious Diseases demonstrated that by 12 months postpartum, the immunogenicity of the vaccine has declined.
“Although maternal antibody protects the newborn infant, high levels of transplacentally acquired antibody might blunt the immune response to active immunization,” Scott A. Halperin, MD, medical director of the Canadian Center for Vaccinology and professor in the departments of pediatrics and microbiology and immunology at Dalhousie Medical School, and colleagues wrote in the study.
Halperin and colleagues conducted a randomized, controlled, observer-blind, multicenter clinical trial to measure the safety and immunogenicity of Tdap during pregnancy and the effect Tdap has on the infant’s immune response to primary vaccination at 2, 4 and 6 months of age and the booster vaccination at 12 months. The study included 273 women who received either Tdap or tetanus-diphtheria vaccine in the third trimester of pregnancy, and serum was collected from 261 infants for immunogenicity analyses, Halperin and colleagues reported.
According to the results, cord blood levels were 21% higher than maternal pertussis toxoid levels in infants whose mothers received Tdap during pregnancy. Additionally, levels of filamentous hemagglutinin, pertactin and fimbriae were 13%, 4% and 7% higher, respectively, in infants of Tdap recipients than maternal levels. Compared with infants whose mothers received tetanus-diphtheria vaccine, infants of Tdap recipients demonstrated higher levels of pertussis toxoid antibodies at birth and at 2 months and significantly higher levels of filamentous hemagglutinin, pertactin and fimbriae antibodies at birth, 2 months and 4 months.
However, pertussis toxoid and filamentous hemagglutinin antibody levels were significantly lower at 6 and 7 months in infants whose mothers received Tdap. The researchers also observed significantly lower levels of pertactin and fimbriae at 7 months, according to the study. Both groups had similar rates of adverse events, and antibody level differences persisted at 12 months for all pertussis antibodies and post-booster for filamentous hemagglutinin, pertactin and fimbriae.
Halperin and colleagues suggest that Tdap during pregnancy is safe and results in higher levels of antibodies early in infancy. However, they observed lower levels after the primary vaccine series, demonstrating a decline in immunogenicity.
“This study provides new data concerning the blunting of the immune response to active, primary series immunization in infants of women immunized with Tdap during pregnancy,” Halperin and colleagues wrote.
They called the clinical significance of the blunted immune response “unclear.”
“If antibody levels after the primary series are lower in infants of women immunized with Tdap, this could lead to an increased burden of pertussis disease in the second half of the first year of life or afterward,” they wrote. “Although there is a potential for increased number of pertussis cases in later infancy, these are not usually associated with mortality; therefore, this outcome may be acceptable if pertussis deaths in early infancy are prevented.” – by Marley Ghizzone
Disclosures: Halperin reports receiving personal fees from GlaxoSmithKline and Sanofi Pasteur and having a patent related to adjuvants for pertussis vaccines. Please see the study for all other authors’ relevant financial disclosures.