Abstract
BackgroundAlthough strategies to contain influenza pandemics are well studied, the characterization and the implications of different geographical and temporal diffusion patterns of the pandemic have been given less attention.Methodology/Main FindingsUsing a well-documented metapopulation model incorporating air travel between 52 major world cities, we identified potential influenza pandemic diffusion profiles and examined how the impact of interventions might be affected by this heterogeneity. Clustering methods applied to a set of pandemic simulations, characterized by seven parameters related to the conditions of emergence that were varied following Latin hypercube sampling, were used to identify six pandemic profiles exhibiting different characteristics notably in terms of global burden (from 415 to >160 million of cases) and duration (from 26 to 360 days). A multivariate sensitivity analysis showed that the transmission rate and proportion of susceptibles have a strong impact on the pandemic diffusion. The correlation between interventions and pandemic outcomes were analyzed for two specific profiles: a fast, massive pandemic and a slow building, long-lasting one. In both cases, the date of introduction for five control measures (masks, isolation, prophylactic or therapeutic use of antivirals, vaccination) correlated strongly with pandemic outcomes. Conversely, the coverage and efficacy of these interventions only moderately correlated with pandemic outcomes in the case of a massive pandemic. Pre-pandemic vaccination influenced pandemic outcomes in both profiles, while travel restriction was the only measure without any measurable effect in either.ConclusionsOur study highlights: (i) the great heterogeneity in possible profiles of a future influenza pandemic; (ii) the value of being well prepared in every country since a pandemic may have heavy consequences wherever and whenever it starts; (iii) the need to quickly implement control measures and even to anticipate pandemic emergence through pre-pandemic vaccination; and (iv) the value of combining all available control measures except perhaps travel restrictions.
Highlights
The continuous spread of H5N1 avian influenza raises concerns about the possible consequences of a major human influenza pandemic
The choice of the number of clusters was based on the values of three criteria: the pseudo t2 statistics, the squared multiple correlation R2-accounting for the proportion of variance explained by the clusters- and the cubic clustering criterion Cubic Clustering Criterion (CCC) which compares the observed R2 to the expected R2 from a uniform distribution
Clustering the first set of 1000 simulations identified six groups of pandemic profiles that could occur in the absence of any control measure
Summary
The continuous spread of H5N1 avian influenza raises concerns about the possible consequences of a major human influenza pandemic. Longini et al [4] showed that in the case where interventions were used jointly (targeted antiviral prophylaxis, quarantine and pre-vaccination), the pandemic could be stopped at the source even for basic reproductive numbers as high as 2.4. Our study highlights: (i) the great heterogeneity in possible profiles of a future influenza pandemic; (ii) the value of being well prepared in every country since a pandemic may have heavy consequences wherever and whenever it starts; (iii) the need to quickly implement control measures and even to anticipate pandemic emergence through pre-pandemic vaccination; and (iv) the value of combining all available control measures except perhaps travel restrictions
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