Pertussis is resurging worldwide. In Africa alone it is estimated that there are 2.1 million cases and 542,000 deaths from pertussis in infants under 1 year with the highest rates of morbidity and mortality in infants <3 months old, before possible prevention via the infant immunization programme1. To protect these most vulnerable infants, the World Health Organisation (WHO) recommends Tdap vaccination as safe in pregnancy and recommends the use of wP vaccines within the EPI. Maternal antibody following aP vaccination can interfere with infant anti-pertussis antibody responses post infant EPI vaccination, which is of concern in high burden settings such as Uganda. There are therefore multiple factors in this population which may influence the effect of pertussis immunization in pregnancy, and which have not been studied, most notably HIV infection and interference with wP vaccines in infants. The immunogenicity of Tdap in HIV-infected pregnant women has not yet been examined. In addition, to date, the effect of maternal vaccination, placental transfer and infant antibody responses in HEU infants have not been studied at all. There are no studies examining the immune response to wP vaccine administered to infants (EPI recommendation) whose mothers received aP in pregnancy.

Inclusion Criteria:

• Participant must be a woman aged 18 years or older, inclusive at day of signing the ICF;
• Pregnant woman at >16 and <26 weeks gestation, verified by ultrasound scan;
• Documented HIV test during pregnancy taken by rapid test at the screening visit;
• Low risk, singleton pregnancy, as assessed by the study physician based on ultrasound scan and previous obstetric history; and
• The woman is willing to comply with the study procedures, including giving birth at Kawempe National Referral Hospital, remaining in the study area until the infant is 1 year old and is able to provide informed consent for herself and on behalf of the infant

Exclusion Criteria:

Any of the following:

• Previous anaphylaxis to any component of Td or Tdap vaccines;
• vaccination is otherwise contraindicated (per product monographs);
• Documented to have received four or more previous tetanus toxoid vaccine doses (as this would prevent randomisation to Tdap group and receipt of two additional tetanus toxoid containing vaccines);
• History of pre-eclampsia or eclampsia in previous pregnancies;
• Gestational diabetes in current pregnancy;
• Rhesus negative mothers;
• Multigravida;
• Previous late stillbirth (defined as loss of pregnancy at any time after 28 weeks gestation);
• Previous low birth weight baby of less than 2.0 kilograms or premature delivery (defined as a delivery before 37 weeks gestation);
• Previous neonatal death (defined as death of an infant within the first 28 days of life);
• Previous delivery of an infant with a known or suspected genetic or chromosomal abnormality;
• History of other significant pregnancy related complications judged likely to affect the safety of the mother or infant or to significantly compromise the endpoint data collected;
• History of other significant neonatal complications judged likely to affect the safety of the mother or infant or to significantly compromise the endpoint data collected;
• Significant maternal chronic illness including but not limited to hypertension requiring treatment, heart disease, lung disease, neurological disorders including a history of epilepsy or recurrent afebrile seizures, kidney disease, liver disease, anaemia and other haematological disorders (including sickle cell), endocrine disorders including known diabetes mellitus, autoimmunity;
• Severe anaemia (less than 7.0g/dL);
• Known Syphilis or hepatitis B (HBV) virus positive or found to be Syphilis or HBV positive during screening;
• Any other condition judged to significantly increase the risks to either the mother or the infant within the current pregnancy (including relevant history from previous pregnancies);
• Receipt of any blood product including human immunoglobulins at any stage during the current pregnancy or plan to receive any blood products during the period or trial participation (receipt of blood products in an emergency or for obstetric reasons will not represent a protocol deviation given such situations are unplanned);
• Clinically suspected or confirmed congenital or acquired clotting or bleeding disorders or the current receipt of medications known to alter clotting or bleeding;
• Any clinically significant signs or symptoms of acute illness, significant abnormalities in vital signs, an axillary temperature of greater than 38.0°C or any recorded fever (greater than 38.0°C) in the preceding 24 hours;
• Two or more symptoms (nausea/vomiting, diarrhoea, headaches, fatigue and myalgia) rated as grade 2 and clinically significant on the maternal systemic reactogenicity scale present at baseline on the day of vaccination;
• Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily;
• Participation in the 4 weeks preceding the trial vaccination or planned participation during the present trial period in another clinical trial investigating a vaccine, drug, medical device, or medical procedure;
• History of being treated for pertussis

Study nursing staff and participants will be blinded to the vaccine given and vaccine syringes will be covered with an opaque label, obscuring the vaccine. Only the preparing pharmacist will be aware of the vaccine used. A study nurse who is blinded to the vaccine given will observe for immediate reactions to the vaccine in a separate room from where the woman will receive her vaccination. This room will have an emergency trolley with appropriate drugs available should these be required.

The laboratory-based research team conducting the assays will be blinded to subject allocation.