Implications of spatially heterogeneous vaccination coverage for the risk of congenital rubella syndrome in South Africa

C J E Metcalf,O N Bjørnstad,P Klepac,B T Grenfell,J M Mcanerney,J Lessler,A Puren,C Cohen,A Tatem,G M Ntshoe

doi:10.1098/rsif.2012.0756

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.

Highlights

Rubella is a mild infection if contracted during childhood, but infection during early pregnancy can lead to birth of a child with congenital rubella syndrome (CRS), entailing numerous potential disabilities with substantial financial and social costs [1,2]
While the burden of CRS may be small relative to the overall disease burden of children in certain regions, the low cost of the rubella vaccine, the relatively low transmission rate of the infection compared with measles and the ability to deliver vaccine without administering an extra shot mean that it may be one of the diseases most effectively tackled
The classic concern for rubella vaccination has been that insufficient vaccination coverage of children may lead to an rsif.royalsocietypublishing.org J R Soc Interface 10: 20120756 (a) 0.40 (b) 12

Summary

Introduction

Rubella is a mild infection if contracted during childhood, but infection during early pregnancy can lead to birth of a child with congenital rubella syndrome (CRS), entailing numerous potential disabilities with substantial financial and social costs [1,2]. Unless control measures are synchronized within a state or a broader region, there is a 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 [6]. Exposure through rare contacts with infected individuals from communities in which vaccine coverage is low enough to allow rubella to circulate could occur, enhancing the CRS rate In this way, age-specific risk of a disease is affected by vaccine-induced heterogeneities in circulation, operating either via spatial heterogeneities in vaccine cover or via homogeneous vaccine cover of sufficient magnitude to break the chains of transmission and push communities below the critical community size (e.g. the population size above which immunizing childhood infections are not vulnerable to stochastic extinction [7])

Methods

Results

Conclusion