Doctoral Degrees (Epidemiology and Biostatistics)

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Browsing Doctoral Degrees (Epidemiology and Biostatistics) by browse.metadata.advisor "Metcalf, C. Jessica E."

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    Burden of congenital rubella syndrome and potential impact of rubella vaccine introduction in South Africa
    (Stellenbosch : Stellenbosch University, 2021-12) Motaze, Nkengafac Villyen; Wiysonge, Charles S.; Suchard, Melinda S.; Metcalf, C. Jessica E.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Global Health. Epidemiology and Biostatistics.
    ENGLISH SUMMARY : Background: Introduction of rubella vaccines into public vaccination schedules of all countries is necessary if global rubella elimination is to be achieved. Rubella is targeted for elimination in five World Health Organization (WHO) regions and several international organizations, under the stewardship of the WHO, are working towards this goal. Although there is no rubella elimination or control target for the WHO Africa region, there has been accelerated introduction of rubella vaccination on the continent. South African government is planning to introduce rubella vaccination in its Expanded Programme on Immunization (EPI) schedule and several epidemiological studies have been conducted to aid preparation of this public health intervention. In the absence of vaccination, rubella is mainly a mild endemic childhood viral illness that is asymptomatic in up to 50% of cases. The most severe consequences of rubella occur when infection occurs during pregnancy. These include miscarriages, stillbirths, intra-uterine growth restriction and congenital rubella syndrome. Rubella vaccines are therefore intended to prevent rubella and associated complications. In South Africa, rubella vaccines are not part of the EPI schedule and there is limited information on the epidemiology of rubella and its complications. In addition, the South African government has to cover the cost of introducing rubella vaccination. Therefore, the aim of this research project was to characterize the epidemiology of rubella and congenital rubella syndrome in South Africa, to assess the potential impact of introducing rubella vaccination in the EPI schedule. Methods: Four different studies were carried out as part of this PhD project: a cross-sectional descriptive study, a sero-survey, a mathematical modelling study and a systematic review. Results: The findings of a newly established CRS surveillance system to provide data on disease trends in the absence of rubella vaccination are presented in the first research component. We provided baseline data on laboratory-confirmed CRS that will enable planning and monitoring of RCV implementation in the South African EPI program. Ninety-eight percent of mothers of infants with CRS were young women 14 to 30 years old, indicating a potential immunity gap in this age group for consideration during introduction of RCV. In the second research component, we present results of testing on residual samples collected from public health facilities to identify immunity gaps in various age groups and genders. The bulk of individuals susceptible to rubella are children under sixteen years old and about 20% of individuals 16 to 49 years old are susceptible to rubella. In multivariable logistic regression, age and province of residence were found to be associated with rubella susceptibility.Webuilt on a previously published mathematical model adapted to the South African context in the third research component and provide insights into optimal scenarios for RCV introduction into the South African public immunization schedule. We simulated a number of scenarios that combined infant vaccination with vaccination of older individuals. Routine vaccination at 12 months of age coupled with vaccination of nine-year-old children was associated with the lowest RCV cost per CRS case averted for a similar percentage CRS reduction. Interestingly, at 80% RCV coverage, all vaccine introduction scenarios could achieve rubella and CRS elimination in South Africa.In the final research component, we systematically reviewed mathematical modelling studies to identify the most effective approach for countries introducing RCV into their public immunization schedules. There were variations in the manner in which individual studies reported outcomes. However, we found that better outcomes are obtained when rubella vaccination is introduced into public vaccination schedules at coverage figures of 80%, as recommended by WHO, or higher. Conclusion: The results from these different studies support the implementation of a strategy involving infant vaccination in combination with vaccination of older individuals. Further research projects are required to provide more detail on the burden of CRS and the economic impact of RCV introduction into the EPI schedule.