Human live-attenuated rotavirus to assess next-genchallenge with eration rotavirus vaccines in Africa

Rotavirus infection causes severe diarrhoea and is responsible for about 130,000 child deaths every year in low-income countries in Africa and Asia. Two vaccines have recently been introduced worldwide and have started to reduce the burden of rotavirus disease. Unfortunately, these orally administered vaccines are less effective in the low-income countries where they are needed compared with high-income countries. This means rotavirus remains the main cause of hospitalisation for diarrhoea even after their introduction.

To tackle this challenge, we need a next-generation of rotavirus vaccines that overcome the barrier to effective oral vaccines in low-income countries. These vaccines are in the development pipeline. However, their assessment in clinical trials is challenging because comparison with placebo is no longer considered ethical and immune correlates of protection (CoP) that could be used as alternative trial endpoints have not been identified.

Controlled human infection studies, where participants are deliberately exposed to wild-type or attenuated infections, are increasingly playing a role in the clinical development of new vaccines and global recommendations concerning their use.

We propose to use a licensed live-attenuated oral rotavirus vaccine (Rotarix) as a controlled human infection challenge in infants in Zambia to investigate a novel injectable rotavirus vaccine used alone or in combination with oral vaccination. This is an exciting opportunity to see whether this injectable VP8 subunit vaccine can overcome the barrier to oral immunisation and whether its effectiveness is improved through combined use with oral vaccine.

Use of a live-attenuated vaccine as a challenge agent has many advantages compared with wild-type infection, including its established safety profile, highly regulated (GMP) manufacture and its suitability for use in children. The relevance of this infection model (rather than clinical disease) is supported by recent findings showing acquired immunity to rotavirus acts primarily by preventing infection rather than reducing the risk of disease following infection and will be further validated by comparison with results from an ongoing phase 3 clinical trial of the efficacy of this vaccine.

This human infection model will also allow us to investigate the development of intestinal (mucosal) immunity following oral and parenteral immunisation and to efficiently explore potential immune correlates of protection (CoP) against infection that can be measured in blood or saliva samples taken from infants after vaccination. These will be based on recent advances in our understanding of rotavirus immunology and focus on systemic and mucosal antibodies targeting different rotavirus antigens.

If we find that combined use of an oral and injectable vaccine is more effective than current schedules, this will support further studies and programmatic evaluation that could ultimately lead to a greater impact of vaccination in Africa and Asia on rotavirus disease and mortality. At the end of this project, we will also have improved our understanding of vaccine-induced rotavirus immunity and established a live-attenuated rotavirus infection model in African infants that can be used to assess new rotavirus vaccines under development.

Widespread introduction of oral rotavirus vaccines (ORVs) in Africa has reduced diarrhoeal disease and mortality, but rotavirus remains the leading cause of hospitalised disease as these vaccines are only ~50% effective in low-income countries compared with ~90% in high-income countries. Testing the next-generation of vaccines is challenging because very large trials are needed to establish non-inferiority/superiority and reliable immune correlates of protection (CoPs) have not been identified. Building on pilot work in Zambia, we propose to measure rotavirus shedding after challenge with live-attenuated rotavirus vaccine (Rotarix) to assess mucosal immunity induced by a novel parenteral trivalent VP8 subunit vaccine (SK Chemicals, South Korea) used alone or in combination with ORV. Administration of parenteral VP8 vaccine in a combined schedule promises to maximise protection by boosting immunity in 'mucosally-primed' infants and immunising those that remain naïve. The appropriateness of this human infection model is supported by recent work showing protection against rotavirus disease is mediated by immunity against infection rather than against disease following infection. Also, we will use this novel and safe human infection challenge model to investigate the development of mucosal immunity and measure novel immune CoPs against infection, which can be validated by comparison with stored samples from the ongoing phase 3 efficacy trial of VP8 vaccine against clinical disease. Identification of CoPs as potential alternative clinical trial endpoints and the establishment of a rotavirus infection human challenge model in Africa would greatly facilitate the testing and licensure of RVs under development. More immediately, if we find that combined oral-parenteral immunisation is effective, subsequent programmatic evaluation could support wider introduction of this schedule in Africa.

In addition to the academic beneficiaries noted above, our work will benefit the following groups:

The general public in low- and middle-income countries (LMICs)
Children and their families in LMICs who suffer >99% of all deaths due to rotavirus diarrhoea are the primary target beneficiaries of this research project. Demonstration of safe and effective immunisation with trivalent VP8 subunit vaccine and Rotarix in a combined schedule may lead to programmatic evaluation and potentially subsequent adoption in routine immunisation programmes. This could lead to a reduction in the remaining burden of rotavirus disease that persists despite global scale-up of access to existing rotavirus vaccines. Programmatic evaluation could immediately follow our research project, leading to an expected impact in LMICs within approximately 5 years of completion of the research. These LMICs are on the DAC list of ODA recipients and our work is therefore ODA compliant.

Public health organisations and national governments
Evaluation of an alternative rotavirus vaccination schedule using a vaccine that is currently undergoing phase 3 efficacy testing will benefit national and international public health organisations, national governments and policy-makers. Even if protection and immunogenicity of a combined schedule is not better than Rotarix or VP8 subunit vaccine alone, data generated from our research will support decision making around the introduction of VP8 vaccine in Africa. Increasing the number of vaccine options would help support a healthy market. In addition, information on the immunogenicity and safety of a single dose of trivalent VP8 vaccine alongside Rotarix would increase the number of vaccination options with potential implications for cost saving.

Industry and international health organisations
We will establish a live-attenuated rotavirus human infection challenge model at CIDRZ in Zambia. This will be of benefit to industry, international health organisations (e.g. PATH, BMGF) and universities developing new rotavirus vaccines, including live-oral, inactivated, virus-like particle and engineered protein vaccines. At the end of the project CIDRZ will be in a position to assess the immunogenicity and protection against challenge offered by these vaccine candidates (given appropriate regulatory and ethical review following phase 1 testing). This is valuable and timely given the ethical challenges to using placebo in randomised controlled trials of protection against disease following natural exposure. Additionally, our proposed study of vaccine-induced correlates of protection against infection after challenge, including minimally invasive sample collection (e.g. saliva), will help support trials of rotavirus vaccines using alternative endpoints.

CIDRZ and partner institutions
The research project and assessment of a rotavirus human infection challenge model will be of direct benefit to CIDRZ in Zambia. As part of the research project investigator laboratories will support staff training and transfer immunology expertise, laboratory protocols and data analysis methods. Staff employed on the project will benefit from mentorship from the study investigators. Previous award of an MRC HIC-Vac pump-priming award to Chilengi on rotavirus human infection models has already supported establishment of key rotavirus serology and shedding assays at CIDRZ. Further development of ELISA and neutralisation assays for VP8, VP5 and VP7-specific antibodies (Iturriza-Gomara - University of Liverpool) and micro-modified ELISPOT assays (Czerkinsky - IPMC-CNRS, France) will be supported through this proposed project. In addition to training and workshops, QC/QA for these assays will be provided.