Pertussis (Tdap) Vaccination in Pregnancy

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.