Despite good vaccination coverage, included in national immunization programs in developed countries, the number of reported pertussis cases is rising, also in very young infants. Current immunization strategies fail to protect infants too young to be immunized with the licensed vaccine. Different strategies are possible to close the gap of susceptibility between the loss of maternal antibodies and protection by vaccination. The main aim of the present study is to measure the influence of an adult pertussis booster in pregnant women, on the titer and duration of maternal antibodies in their infants. Early humoral immunity will be assessed and the influence on vaccine response of the infant measured. The present study offers the opportunity to have new insights in neonatal immunological mechanisms against pertussis and a better understanding in strategies to protect infants against pertussis.

Inclusion Criteria:

• Women aged 18-35 years
• Willing to be immunized during pregnancy OR
• Received already a pertussis vaccination during pregnancy, as advised by gynaecologist or general practitioner.
• Age matched controls will be identified in the same time period in the recruiting hospital.
• Availability for follow-up visits and phone call access through 16 months following delivery
• Willing to have infant immunized with hexavalent vaccine at 8.12 and 16 weeks and 15 months of age (= normal Belgian schedule) with pediatrician, the general practitioner or at the Centre for the Evaluation of Vaccination.
• In the 18th-32nd week of a pregnancy at low risk for complications as determined by the obstetrician

Exclusion Criteria:Women:

• Serious underlying medical condition
• History of a febrile illness (>= 38° Celsius) within the past 72 hours before injection
• Previous severe reaction to any vaccine
• Receipt of tetanus-diphtheria toxoid immunization within the past 1 month
• Receipt of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis vaccine absorbed (Tdap) immunization in the last 10 years
• Receipt of a vaccine, blood product (excluding Rhogam) or experimental medicine within the 4 weeks prior to injection through 4 weeks following injection
• Receipt of or plans to receive influenza vaccine within the 4weeks prior to or following injection. One month interval should be respected in order to evaluate eventual Adverse events following one of both vaccines (fever, local symptoms).
• High risk for serious obstetrical complication
• Anything in the opinion of the investigator that would put the participant at risk.

Exclusion criteria for the offspring:

• Serious underlying medical condition
• No signed informed consent by both parents
• Severe reactions to any vaccine
• Anything in the opinion of the investigator that would put the participant at risk.