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

Tuesday, 3rd of December 2013

[source]Epidemiology and Infection[|source]

Rubella vaccine has been licensed for nearly 50 years, is highly efficacious and available as combined measles-rubella (MR) or measles-mumps-rubella (MMR) vaccine. However, the challenge of preventing CRS by rubella-containing vaccine (RCV) is complex, because feedbacks between incidence and rate of infection mean that routine infant vaccination (‘universal vaccination’) will tend to increase the average age of infection, although if vaccine coverage is high enough, the age-specific incidence of rubella decreases at all ages. 

In this article, the authors explore minimum coverage required to prevent a CRS increase after introduction of universal rubella vaccination, rooting their analysis in the current public health context, and ranging over the plausible extent of demographic contexts and remaining uncertainties in rubella transmission. The report concludes by asserting that in low-to-average birth-rate contexts, benefits of immunization are likely to be high across a range of levels of routine coverage, especially in the presence of additional immunization activities. The paper maintains that in countries with high birth rates, 80% coverage of routine infant vaccination alone may not remove all risks of adverse events, and therefore funding ought to be guaranteed for high-quality SIAs to continue in addition to routine infant and young children immunization.  More details are available at:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3487482/

 

Abstract

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 modeled 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.