Impact of maternally derived antibodies and infant microbiota on the immunogenicity of rotavirus vaccines in African, Indian and European infants.

Rotavirus is the commonest cause of severe childhood diarrhoea, leading to almost half a million infant deaths worldwide each year. Rotavirus vaccination is recommended by the World Health Organisation for all infants, especially in countries with the highest mortality due to diarrhoeal disease which are in sub-Saharan Africa and in southern Asia, but current vaccines are least effective in the countries where most deaths from diarrhoea occur. The reasons for the inferior vaccine performance are not well understood, but are likely to be complex.
Rotavirus vaccines rely on the oral administration of weakened rotaviruses which multiply in the gut of the baby to stimulate the immune system to produce antibodies and protect the child from developing rotavirus diarrhoea. Factors that affect how well rotavirus vaccines perform may include a) maternal antibodies passed to the baby in the womb or via breast milk (passively-acquired immunity); b) the baby's gut bacteria (microbiota), which is important for maintaining a healthy gut and promoting effective immune responses following natural infection or vaccination and c) giving two oral vaccines together where one virus may interfere with the other. Children living in poor countries are also exposed to many gut infections, which lead to gut inflammation and which may contribute to the inability to respond well to oral vaccines, development of malnutrition and physical and cognitive growth delays.
The key goals of this project are to determine the roles of passively-acquired immunity, the composition of the baby's gut bacteria and the effect of giving two oral vaccines together on immune responses to rotavirus vaccine. The study will follow babies before and after rotavirus vaccination in three countries (Malawi, India and the UK), from birth to 14 to 16 weeks of age. Studies have shown that babies in Malawi and India have poor responses to rotavirus vaccination, whereas children in the UK will have stronger responses leading to protection from rotavirus diarrhoea, as in other high-income countries. We will compare the levels of antibodies transferred from the mothers to the babies during pregnancy and after birth, by measuring the antibodies in the mothers' blood and in their breast-milk. We will study the composition of the gut microbiota from birth to the time of rotavirus vaccination in each of the three groups. We will relate the microbiota composition in the gut of child to that of the mother's gut and breast-milk, and analyse the data taking into account factors such as nutrition and early gut infections, which differ by location, in order to assess how they impact the infant's ability to respond to rotavirus vaccination, and measure the levels of rotavirus antibody generated by the babies after vaccination. We will also carry out a study in India that compares the response to rotavirus vaccine in babies who are given polio vaccines at the same time as the oral rotavirus vaccine by two different routes, orally or by injection. This study is important because there is a global plan to introduce the injectable polio vaccine as part of the plan to eradicate poliovirus. This will help provide a comparison between India and Malawi which uses the oral polio vaccine, and India and the UK which uses the injectable vaccine. We can also compare the effect of giving two oral vaccines together compared with the oral rotavirus vaccine given with the injectable polio vaccine in the same population. These studies will develop the tools for new assays and protocols to ensure that the cross-country comparisons are not affected by differences in the way the studies and the analyses were conducted. The results of these studies will directly inform the design of alternative or complementary strategies to improve the performance of these and other anti-diarrhoea vaccines, with an aim to reduce infant deaths by improving resistance to diarrhoea in infants living in developing countries.

Live, attenuated, orally administered rotavirus (RV) vaccines have the potential to greatly reduce diarrhoea deaths but they work less well in countries where they are needed most. In Sub-Saharan Africa and South Asia, vaccine efficacy is 43-66% compared to >90% in high-income countries. The reasons are not understood, but likely to be complex.
Serum IgA responses are lowest where RV vaccine efficacy is poor, and are used as an imperfect correlate for protection. Vaccine virus shedding in stool indicates "vaccine take", but its predictive value as a correlate of protection has not been explored in low income settings. We will address the following questions:
1. What is the role of maternally derived antibodies on RV vaccine take and serum IgA response in infants?
2. Is dysbiosis at the time of vaccination associated with poor RV vaccine take and serum IgA response in infants?
3. What is the effect of co-administered oral poliovirus vaccine (OPV) on the immunogenicity of RV vaccine in infants in low-income settings?
The study will enrol birth cohorts in three countries: Malawi and India, with infant populations in whom RV vaccine efficacy is poor, and the United Kingdom, where vaccine efficacy is high. In India, two cohorts will be recruited to allow comparison of the effect of OPV and inactivated polio vaccine on RV vaccine immunogenicity in the same population. Infants will be followed from birth up to 16 weeks of age. Blood and breast milk samples will be collected to investigate the impact of maternal antibody transfer on seroconversion. Serial stools will examine gut microbiota development, early exposure to natural RV infection and RV vaccine virus shedding post immunisation. Gut and systemic inflammation at the time of vaccination will be assessed. An improved understanding of RV vaccine performance will inform strategies for delivery and design of rotavirus and other enteric vaccines in low-income settings with high burden of enteric infection.

This study will primarily benefit infants living in low income countries by identifying reasons for poor efficacy of live attenuated rotavirus vaccines, which can then be addressed through specific interventions. Improved performance of rotavirus vaccines will directly impact on infant mortality and improve health and quality of life of children living in the poorest countries. Increasing rotavirus vaccine efficacy will also result in improved cost benefit analyses in countries that are or will be investing significant proportions of their limited resources on the introduction of rotavirus vaccination.
In the short term, studying different populations and accounting for their different risk factors will inform the design of appropriate interventions and future clinical trials aimed at improving RV vaccine efficacy among infants living in sub-Saharan Africa and South East Asia. Such interventions, may involve: (a) Changes to vaccine dosing to overcome inhibition of vaccine take by maternally derived immunity; (b) Maternal or new-born vaccination to prevent disease in the neonatal period up to the age of current vaccination; (c) Bringing forward the switch to inactivated poliovirus vaccine to avoid competition between two oral vaccines given concomitantly (oral polio and rotavirus vaccines are currently being currently co-administered in Africa and potentially in south East Asia); (d) Interventions aimed at promoting a "healthy" microbiota in the infant gut leading to improved vaccine efficacy and resistance to enteric disease. These would impact on vaccine manufacturers, and on vaccination policies driven by national departments of health and WHO.
This study will provide novel data on the maternal microbiota imprinting of the infant gut microbiota in different populations, which will inform the most effective approach for targeting interventions for improved gut health and prevention of disease though enhanced immune responses. In the longer term the results and findings derived from this study are likely to be applicable to other enteric infections and vaccines. Enhanced enteric vaccine efficacy in children in resource poor settings will have significant impact beyond reducing infant mortality and morbidity associated with vaccine preventable enteric pathogens. Treating/ preventing dysbiosis which leads to inflammation and impaired immune responses is likely to promote resistance to infection or reduce disease severity associated with enteric pathogens. The resolution of dysbiosis and the reduction of enteric infectious disease will also directly impact on other important morbidities including malnutrition, leading to far reaching health improvements, such as reduction of infant morbidity and mortality, increase health and quality of life resulting in longer term advancements in productivity and the economies of low income countries.
In addition this project will serve as a platform for multilateral capacity building, providing training for Malawian and Indian clinical and laboratory scientists by mentoring and cross-institutional training, including formal workshops lead by Indian and UK investigators in Vellore and Malawi