Epidemiology and Infection

Original Papers

Rubella vaccination

Impact of birth rate, seasonality and transmission rate on minimum levels of coverage needed for rubella vaccination

C. J. E. METCALFa1a2 c1, J. LESSLERa3, P. KLEPACa2, F. CUTTSa4 and B. T. GRENFELLa2a5

a1 Department of Zoology, Oxford University, Oxford, UK

a2 Department of Ecology and Evolutionary Biology, Eno Hall, Princeton University, Princeton, NJ, USA

a3 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore MD, USA

a4 Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, UK

a5 Fogarty International Center, National Institutes of Health, Bethesda, MD, USA

SUMMARY

Childhood rubella infection in early pregnancy can lead to fetal death or congenital rubella syndrome (CRS) with multiple disabilities. Reduction of transmission via universal vaccination can prevent CRS, but inadequate coverage may increase CRS numbers by increasing the average age at infection. Consequently, many countries do not vaccinate against rubella. The World Health Organization recommends that for safe rubella vaccination, at least 80% coverage of each birth cohort should be sustained. The nonlinear relationship between CRS burden and infection dynamics has been much studied; however, how the complex interaction between epidemic and demographic dynamics affects minimum safe levels of coverage has not been quantitatively evaluated across scales necessary for a global assessment. We modelled 30-year CRS burdens across epidemiological and demographic settings, including the effect of local interruption of transmission via stochastic fadeout. Necessary minimum vaccination coverage increases markedly with birth and transmission rates, independent of amplitude of seasonal fluctuations in transmission. Susceptible build-up in older age groups following local stochastic extinction of rubella increased CRS burden, indicating that spatial context is important. In low birth-rate settings, 80% routine coverage is a conservative guideline, particularly if supplemented with campaigns and vaccination of women of childbearing age. Where birth and transmission rates are high, immunization coverage must be well above 80% and campaigns may be needed. Policy-makers should be aware of the potential negative effect of local extinction of rubella, since heterogeneity in vaccination coverage will shape extinction patterns, potentially increasing CRS burdens.

(Received November 30 2011)

(Revised December 30 2011)

(Accepted January 16 2012)

(Online publication February 16 2012)

Key words

  • CRS;
  • demography;
  • extinction;
  • rubella;
  • seasonality;
  • vaccine coverage

Correspondence:

c1 Author for correspondence: Dr C. J. E. Metcalf, Department of Zoology, Oxford University, Oxford, OX1 3PS, UK. (Email: charlotte.metcalf@zoo.ox.ac.uk)

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