The reproduction number of seasonal influenza epidemics in Brazil. 1996-2006

Gerardo Chowell, Cécile Viboud, Lone Simonsen, Mark Miller, Wladimir T. Alonso

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


The transmission dynamics of influenza in tropical regions are poorly understood. Here we explore geographical variations in the reproduction number of influenza across equatorial, tropical and subtropical areas of Brazil, based on the analysis of weekly pneumonia and influenza (P&I) mortality time series in 27 states. The reproduction number (R) was low on average in Brazil (mean = 1.03 (95% CI 1.02-1.04), assuming a serial interval of 3 days). Estimates of the reproduction number were slightly lower for Brazil than for the USA or France (difference in mean R -0.08, p<0.01) and displayed less between-year variation (p < 0.001). Our findings suggest a weak gradient in the reproduction number with population size, where R increases from low population in the North to high population in the South of Brazil. Our low estimates of the reproduction number suggest that influenza population immunity could be high on average in Brazil, potentially resulting in increased viral genetic diversity and rate of emergence of new variants. Additional epidemiological and genetic studies are warranted to further characterize the dynamics of influenza in the tropics and refine our understanding of the global circulation of influenza viruses.

Original languageEnglish (US)
Pages (from-to)1857-1866
Number of pages10
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1689
StatePublished - Jun 22 2010


  • Brazil
  • Geography
  • Influenza
  • Mortality
  • Reproduction number
  • Tropics

ASJC Scopus subject areas

  • Immunology and Microbiology(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Environmental Science(all)
  • Agricultural and Biological Sciences(all)


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