The central aim of this study is to investigate the optimal timing of vaccination in pregnant women. Therefore, pregnant women will be vaccinated against pertussis at different timepoints and blood and breast milk samples will be taken at several timepoints. The main objectives are to assess the impact of timing on humoral and cellular immune responses in pregnant women, on antibody characteristics transferred across the placenta and on transplacental transport efficiency. The impact of maternal pertussis vaccination and timing of maternal pertussis vaccination on breastmilk antibody composition will also be investigated, as well as the impact of vaccination during pregnancy on the mucosal uptake of breastmilk IgA antibodies by the infant respiratory and gastrointestinal tract.

Inclusion Criteria:

• Ability to provide informed consent.
• Willing to be vaccinated with a Tdap vaccine during pregnancy.
• Intend to be available for follow-up visits and phone call access until 6 months postpartum.
• Influenza and COVID-19 vaccination during pregnancy (as per Belgian recommendations) is allowed.

Exclusion Criteria:

• Vaccinated with an aP containing vaccine during the last 5 years
• Significant mental illness (e.g. schizophrenia, psychosis, major depression)
• Serious underlying immunological condition (e.g. immunosuppressive disease or therapy, human immunodeficiency virus (HIV) infection…).
• Systemic treatment with immune suppressive medication, including chronic steroid use of > 10 mg prednisone or equivalent.
• Anything in the opinion of the investigator that would prevent volunteers from completing the study or put the volunteer at risk.
• Previous severe reaction to any vaccine
• High risk for serious obstetrical complications.

Female pregnant population within Flanders