WHAT'S NEW THIS SATURDAY: MODELING CRS RISK FOR SOUTH AFRICA

Thursday, 22nd of November 2012

• IMPLICATIONS OF SPATIALLY HETEROGENEOUS VACCINATION COVERAGE FOR THE RISK OF CONGENITAL RUBELLA SYNDROME IN SOUTH AFRICA

 

1. 1.    C. J. E. Metcalf1,2⇓,
2. 2.    C. Cohen3,4,
3. 3.    J. Lessler5,
4. 4.    J. M. McAnerney3,
5. 5.    G. M. Ntshoe6,
6. 6.    A. Puren6,7,
7. 7.    P. Klepac8,
8. 8.    A. Tatem2,9,
9. 9.    B. T. Grenfell2,8 and

10. O. N. Bjørnstad2,10

+ Author Affiliations

1. 1.    ¹Department of Zoology, Oxford University, Oxford, UK
2. 2.    ²Fogarty International Center, National Institute of Health, Bethesda, MD, USA
3. 3.    ³Centre for Respiratory Disease and Meningitis, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa
4. 4.    ⁴School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
5. 5.    ⁵Department of Epidemiology, John Hopkins Bloomberg School of Public Health, Baltimore, MA, USA
6. 6.    ⁶Centre for Vaccines and Immunology, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa
7. 7.    ⁷Division of Virology and Communicable Diseases, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
8. 8.    ⁸Department of Ecology and Evolutionary Biology, Princeton University, Eno Hall, Princeton, NJ, USA
9. 9.    ⁹Department of Geography, and Emerging Pathogens Institute, University of Florida, Gainesville, FL, USA

10.  ¹⁰Centre for Infectious Disease Dynamics, The Pennsylvania State University, 208 Mueller Lab, University Park, PA, USA

1. e-mail: charlotte.metcalf@zoo.ox.ac.uk

Full text is available at http://rsif.royalsocietypublishing.org/content/10/78/20120756.long

 

 

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.

From conclusions:

To conclude, data available for South Africa shed light on basic aspects of rubella epidemiology (CCS, connectivity, seasonality), but also highlight areas of consideration in a public health setting, including metapopulation-induced changes in age-incidence, which can lead to public health equity issues. The methods we have developed could be use to explore the impact of heterogeneous vaccination in other connectivity contexts and for other infections with an age-specific impact, such as mumps. Interestingly, our model predictions are broadly positive relative to the introduction of routine rubella vaccination in South Africa, despite the relatively low measles vaccine coverage levels explored, with possible relevance to a number of countries in the region. Of course, these conclusions rest on the model assumptions (detailed above), and the data available. Model misspecification is always a risk, and key areas for future research include further detail on the age-transmission profile of rubella in developing and middle-income country settings.