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

Gerardo Chowell*, Cecile Viboud, Lone Simonsen, Mark Miller, Wladimir J Alonso

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

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
JournalProceedings of the Royal Society B: Biological Sciences
Volume277
Issue number1689
Pages (from-to)1857-1866
ISSN0962-8452
DOIs
Publication statusPublished - 2010
Externally publishedYes

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