Development of a Live Attenuated Rotavirus Vaccine as a Human Infection Challenge Model

Diarrhoeal disease is a leading cause of morbidity and mortality in young children, particularly those living in the developing countries of South Asia and sub-Saharan Africa1. Rotavirus is the most common causative agent of moderate to severe diarrhoea in children under age five, responsible for an estimated 215,000 infant deaths every year, most of which occur within lower and middle-income countries (LMICs)2. The widespread introduction of two World Health Organisation (WHO)-approved rotavirus vaccines , RotarixTM, (GlaxoSmithKline Biologicals, Belgium) and RotaTeq, (Merck and Co, New Jersey), has contributed substantially to reducing the number of rotavirus-associated hospitalisations and deaths3-18. However, even with these gains, rotavirus vaccines have repeatedly demonstrated lower immunogenicity, effectiveness, efficacy and duration of protection in children living in LMICs as compared to high-income countries19,20,21. Thus, even after the introduction of rotavirus vaccines (RV), rotavirus remains the leading cause of diarrhoeal morbidity and mortality within these settings. Improved RV would result in substantially greater reductions in diarrhoeal disease morbidity and mortality among infants; there is, therefore, an urgent need to understand the reduced performance of currently available live attenuated oral vaccines in LMICs, to inform and accelerate the development of maximally effective therapeutics.

Recent studies have suggested that alternative schedules could also enhance immunogenicity and eventual vaccine performance in LMICs22,23. In addition, new RV candidates with alternative routes of administration are under development, and show promise for improved vaccine performance21,24,25. However, traditional pathways for licensure of new vaccines that are in the development pipeline through clinical trials have become challenging, with placebo-controlled trials no longer considered ethical, and field efficacy trials requiring increasingly larger cohorts to compare new candidates against existing vaccines. Human Infection Challenge (HIC) models have historically been employed to accelerate vaccine development and offer an opportunity to study both pathogenesis and vaccine immunogenicity mechanisms particularly in human-restricted pathogens. HIC models have not been widely used and accepted in LMICs even though there are scientific and ethical merits of considering the unique opportunity this methodology offers.

We propose to explore the methodological development of an attenuated vaccine as a HIC model to advance rotavirus immunology and vaccinology in Zambian infants. We will also evaluate the use of minimally invasive procedures, including collection of saliva for antibody measurement and stool samples for vaccine virus shedding as measures of vaccine-induced mucosal immunity.

Objective 1 To profile rotavirus specific IgA and IgG responses to vaccination and determine correlation between serum and saliva.

Specific Objective 1a: To profile rotavirus specific IgA and IgG responses at baseline (Day 0), pre-dose 2 (day 28) and 1 month post dose 2 (day 56) in serum and saliva to determine seropositivity and vaccine seroconversion.

Objective 2 To profile cytokine immune responses and determine correlation between serum and saliva.

Specific objective 2a: Determine cytokine profiles in serum and saliva at baseline (Day 0) and track their association with vaccine seroconversion (day 56).

Specific objective 2b: To profile cytokine responses immediately before dose 2 vaccination (day 28), and at 3 days after administration of the second vaccine dose (day 31: rotavirus vaccine challenge).

Objective 3: To assess the relationship of antibody levels in serum and saliva at the time of vaccination (day 0) and on days 28, 31, and 56, against faecal shedding of RV strain in stool collected and on days 3,5,7,14 and 21, and also on day 28 and post dose 2 vaccination days 31, 33, 35, 42, 49 and 56.

Objective 4: To profile and characterize the immediate cytokine immune response to the vaccine in saliva collected on day 0 and day 31, in order to determine whether saliva could serve as a satisfactory proxy for serum in evaluating vaccine-induced mucosal immunity.

1. Methodology
2. Study Design An exploratory and observational cohort study following infants receiving two standard doses of live, attenuated, oral Rotarix™ administered at 6 \& 10 weeks. Infants will be enrolled during the routine EPI visit for week 6 immunizations following administration and provision of written informed consent by their mothers/legal guardians. Each infant will remain in the study for up to 56 days during which they will be intensively followed up with study activities and/or scheduled study clinic visits (summarized in Table 1 below).
3. Study site and population The study will be conducted at George Clinic in Lusaka where the government maternal child health (MCH) and antiretroviral therapy (ART) clinics as well as the CIDRZ George Clinical Study Site are co-located. George Clinic has a catchment population of 145,23053 and is located in a typical peri-urban setting in Lusaka within a surrounding slum. We plan to recruit participants as they randomly attend the health facility. CIDRZ has a good research facility already existing at this clinic and below is a schematic image of the site plan.
4. Selection of participants, sampling methods and sample size Sample size Considerations Participants will be randomly selected from mother-infant pairs attending routine antenatal care at George Clinic. As this will be an exploratory and methodological development study, no formal sample size calculations have been undertaken. We have pragmatically decided to enroll 20 infants which is generally acceptable for phase I-type studies. In case of an estimated 10% attrition due to loss to follow up, we have adjusted the sample to recruit 22 infants.