Pertussis vaccination during pregnancy found to increase quantity and quality of antibodies protecting the baby

Researchers at the University of Turku have participated in a study in which vaccinating women with acellular pertussis vaccine in pregnancy boosted the quantity and quality of pertussis-specific antibodies in the early life of infants.

A randomized, controlled, double-blind, phase 4 trial was conducted in the Gambia to evaluate the effect of pertussis immunization in pregnancy on the immunogenicity of primary acellular or whole-cell pertussis vaccines in a west African cohort.

The study was the first to have characterized the interaction between immunization in pregnancy and primary vaccination with different pertussis vaccine types and how it affects the developing immunity in infants. The study was recently published in The Lancet Infectious Diseases.

Pertussis has made a comeback

Pertussis is a highly contagious respiratory disease caused by Bordetella pertussis bacteria. Despite extensive vaccinations, the disease has resurged. The World Health Organization (WHO) estimates that there are 16 million cases annually and approximately 195,000 deaths in children globally. After the COVID-19 pandemic, pertussis has made a spectacular comeback in Europe and many other parts of the world. In Finland, 2,795 laboratory-confirmed cases were notified in 2024, the highest recorded number since 1995.

Two types of pertussis vaccines are currently used in the world: whole-cell vaccines (wPVs) based on killed whole bacteria and acellular vaccines (aPVs) based on one to five purified bacterial antigens. In general, whole-cell vaccines are used in many low- or middle-income countries and acellular vaccines in high-income countries for primary vaccination. For booster vaccinations in adolescents and adults, only acellular vaccines are used.

Immunization in pregnancy is recommended

Since the highest incidence and mortality of pertussis occur in infants, especially those too young to be vaccinated, immunization in pregnancy (IP) is recommended to protect infants in early life against pertussis. Infants are protected by passive immunization via transplacental transfer of maternal antibodies. The IP programs have been effective, and the majority of European countries have adopted this strategy.

However, studies have shown that IP can decrease the antibody responses of infants to their primary diphtheria-tetanus-acellular pertussis (DTaP) vaccination. This phenomenon is called “blunting.” Blunting of vaccine responses has been observed in IgG-antibody concentrations to different pertussis vaccine antigens, specifically, pertussis toxin, filamentous hemagglutinin, and pertactin, and to diphtheria toxin. However, the short-term and long-term implications of blunting remain unclear, partly because there is no internationally accepted immunological correlate of protection.

Therefore, a comprehensive evaluation of the effect of IP on infant immunity that includes functional antibodies and memory-cell responses and compares acellular versus whole-cell pertussis priming series would be informative and help optimize maternal immunization guidelines and infant vaccination schedules.

Vaccinating women in pregnancy is safe

This study conducted in the Gambia was designed to evaluate the effect of IP on the immunogenicity of primary acellular or whole-cell pertussis vaccines in a west African cohort. The findings demonstrated that vaccinating women with diphtheria-tetanus-acellular pertussis vaccine in pregnancy was safe and well tolerated and boosted the quantity and quality of pertussis-specific antibodies in infants in early life.

Although Tdap-IPV (Tetanus, diphtheria, acellular pertussis, polio vaccine) was associated with relative blunting of the immune response to the DTwP (Diphtheria-Tetanus-whole-cell pertussis) primary vaccination series, pertussis-specific antibody quality and memory B-cell responses were nevertheless preserved.

At the University of Turku, Professor and InFLAMES group leader Qiushui He, Project Researcher Alex-Mikael Barkoff and Professor Jussi Mertsola participated in the study.

Assays developed in Turku

The Turku pertussis team has long-term experience in different pertussis studies, one of which includes the long-term impact of maternal immunization on the development of childhood immunity. The team has developed several sensitive assays to measure the quantity and quality of anti-pertussis antibodies.

“It is important that we have participated in the international study and contributed to the study design and implementation. I am happy to see that the functional antibody assays developed in Turku are being used in different vaccine studies conducted in the world,” says Professor He, who heads the Finnish Reference Laboratory for Diphtheria and Pertussis and the European Reference Laboratory for Diphtheria and Pertussis (EURL-PH-DIPE).