Implications of Spatially Heterogeneous Vaccination Coverage for the Risk of Congenital Rubella Syndrome in South Africa

Tuesday, 3rd of December 2013

[source]Journal of the Royal Society Interface[|source]

Unless Rubella control measures are synchronized within a state or a broader region, there is a possible risk that the benefits of reduced disease incidence will be inequitably distributed, and potentially even worsened in some communities. The reason for this risk is that spatial heterogeneity in vaccine coverage may lead to broken chains of transmission and transient local elimination of rubella in certain areas. In turn, women in such communities may then remain susceptible to rubella infection well into their childbearing years.

In this article, the authors use a uniquely detailed spatio-temporal dataset from South Africa to explore both the basic epidemiology of the infection, and the repercussions likely to follow the introduction of a rubella-containing vaccine, using recent measles coverage as a template. The report documents that a global reduction in infectious individuals moving between districts may increase the burden in smaller populations below the critical community size if these are unvaccinated, because of longer waiting times following extinction, making the interaction between population movement, coverage and the critical community size a key equity question. Paper concludes with the reminder on the possible paradoxical effect of raising risk of RCS with sub-optimal rubella vaccination coverage. More details are available at:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3565806/

 

Abstract

Rubella is generally a mild childhood disease, but infection during early pregnancy may cause spontaneous abortion or congenital rubella syndrome (CRS), which may entail a variety of birth defects. Since vaccination at levels short of those necessary to achieve eradication may increase the average age of infection, and thus potentially the CRS burden, introduction of the vaccine has been limited to contexts where coverage is high. Recent work suggests that spatial heterogeneity in coverage should also be a focus of concern. Here, we use a detailed dataset from South Africa to explore the implications of heterogeneous vaccination for the burden of CRS, introducing realistic vaccination scenarios based on reported levels of measles vaccine coverage. Our results highlight the potential impact of country-wide reductions of incidence of rubella on the local CRS burdens in districts with small population sizes. However, simulations indicate that if rubella vaccination is introduced with coverage reflecting current estimates for measles coverage in South Africa, the burden of CRS is likely to be reduced overall over a 30 year time horizon by a factor of 3, despite the fact that this coverage is lower than the traditional 80 per cent rule of thumb for vaccine introduction, probably owing to a combination of relatively low birth and transmission rates. We conclude by discussing the likely impact of private-sector vaccination.