Gambia Pertussis Study (GaPs)

Overview

Currently, there are two types of vaccines available against pertussis (whooping cough), an infectious disease of the respiratory tract that can be extremely serious in very young children. Both have advantages and disadvantages: The acellular form (aP, mainly used in resource-rich countries) does not appear to offer as long lasting protection, but the whole cell vaccine (wP, mainly used in LMIC) appears to be generally more reactogenic. There is consensus that a "better pertussis vaccine" ought to be designed. The GaPs trial is part of a series of clinical trials performed by the PERtussIS COrrelates of Protection Europe (PERISCOPE) Consortium, an EU-funded group of investigators which aims to generate knowledge on immune responses to pertussis. A better understanding of human biomarkers of protective immune responses to B. pertussis and its waning immunity is needed to accelerate the design and testing of new pertussis vaccines with a longer duration of protection. This proposal describes the design and objectives of the clinical trial to be conducted in the Gambia, which is the only site in Africa involved in the consortium and involves the recruitment of 600 mother/infant pairs. Pregnant women will be randomised to receive either the usually recommended tetanus vaccination or a combination vaccine against whooping cough, diptheria, tetanus and polio. Their infants will receive either aP or wP as part of their EPI vaccines, and resulting immune responses will be characterized in detail up to the age of 9 months. The investigators will use immunological assays to investigate the functional humoral and cellular responses to pertussis in infants born to mothers who are randomized to receiving pertussis vaccine in pregnancy or not, and their infants who will receive either aP or wP vaccine. Our research questions are: Does vaccination against pertussis in pregnancy have impact on subsequent immune responses to pertussis vaccine and other EPI vaccines in the infants Does vaccination of infants with wP vaccine induce different levels and functionality of antibody and/or T cell responses than vaccination with aP vaccine What is the difference in innate and acquired immunity- as measured with novel systems vaccinology tools- between being vaccinated with wP versus aP?

The investigators are conducting a randomised, controlled, double-blinded, clinical vaccine trial in pregnant women combined with an open-label controlled Phase IV clinical vaccine trial in their infants. The trial will examine the differences in immunity generated by aP compared with wP in infants at 5 and 9 months of age, and examine the impact of maternal antibodies on the immune response of infants receiving aP or wP vaccines at two, three and four months. The investigators aim to address two key question: 1. If measures of immunity in infants given aP or wP differ by 5 and 9 months of age; and 2: If and- if so- how maternal pertussis antibodies affect the development and maintenance of immunity to Bordetella pertussis in infants. Rationale for the trial: Pertussis (whooping cough) is an infectious disease that can be very serious- particularly in young infants- but preventable through vaccination. There are two types of vaccines: acellular (aP) and whole cell (wP) vaccines, both extensively used worldwide. A clearer understanding of how these two different types of vaccines work is fundamental when considering adjustments or rethinking vaccination strategies and such knowledge will help the future development of new vaccines, given that some LMIC have already introduced aP but the current WHO recommendation still continues to recommend wP vaccine for those who have not yet switched. Increases in the incidence of pertussis infection, including fatal cases in young infants, have been recently observed in many regions in the world, more likely associated with the use of aP vaccines. As a consequence, it is now recommended in several countries that women should receive aP vaccination in pregnancy so that their high levels of pertussis antibody which will be passed on via the placenta can protect their babies in early life, before the infants have received sufficient doses of pertussis vaccine themselves. However, it is currently unclear if and how maternal antibodies affect long-term immunity to pertussis in infants. Unlike in the UK, where many women of childbearing age would have received aP vaccine in childhood, in The Gambia, all women would have been primed with wP vaccine as part of the NIP. Hence a study in this group of women is uniquely placed to assess if different priming regimens could have different quantitative and qualitative effects on transplacental antibody transfer for pertussis antibody, providing additional insights in comparison to parallel studies in Europe under the PERISCOPE consortium (PERtussIS COrrelates of Protection Europe). A better understanding of human biomarkers of protective immune responses to B. pertussis, and its waning immunity is needed to accelerate the design and testing of new pertussis vaccines with a longer duration of protection. Trial design: The investigators will recruit 600 mother/infant pairs. Following informed consent, sensitisation and eligibility checks including antenatal ultrasound to date the pregnancy, pregnant women will be randomised to receive either Boostrix IPV (contains antigens against pertussis, tetanus, diphteria and polio)- a vaccine recommended for pregnant women in the UK and other countries where recent pertussis outbreaks have been observed, or the tetanus vaccine routinely recommended for women in LMIC. Pre vaccination antibody titres will be measured in the women prior to vaccination between 28-34 week gestation and vaccine responses measured subsequently at the time of giving birth. Cord blood will be collected to measure transfer of maternal antibody. Infants will be grouped to receive either aP or wP at 2,3 and 4 months of age, in line with routine EPI programs. Blood samples will be collected from infants prior to vaccination and following doses of vaccines at specific intervals to measure innate and acquired immune responses and followed up until 9 months of age. Infants will be allocated to subgroups for blood tests so that no infant will have between 4 and max 5 episodes of blood sampling up to the age of 9 months. Samples will be processed for quantitative and qualitative antibody, innate and acquired cellular immune responses. Where available, samples will be stored for further investigations using transcriptomic and epigenetic methodologies. Samples, results and data will be shared with the PERISCOPE consortium members.