Abstract
BackgroundCo-circulation of influenza strains is common to seasonal epidemics and pandemic emergence. Competition was considered involved in the vicissitudes of co-circulating influenza strains but never quantitatively studied at the human population level. The main purpose of the study was to explore the competition dynamics of co-circulating influenza strains in a quantitative way.MethodsWe constructed a heterogeneous dynamic transmission model and ran the model to fit the weekly A/H1N1 influenza virus isolation rate through an influenza season. The construction process started on the 2007–2008 single-clade influenza season and, with the contribution from the clade-based A/H1N1 epidemiological curves, advanced to the 2008–2009 two-clade influenza season. Pearson method was used to estimate the correlation coefficient between the simulated epidemic curve and the observed weekly A/H1N1 influenza virus isolation rate curve.ResultsThe model found the potentially best-fit simulation with correlation coefficient up to 96% and all the successful simulations converging to the best-fit. The annual effective reproductive number of each co-circulating influenza strain was estimated. We found that, during the 2008–2009 influenza season, the annual effective reproductive number of the succeeding A/H1N1 clade 2B-2, carrying H275Y mutation in the neuraminidase, was estimated around 1.65. As to the preceding A/H1N1 clade 2C-2, the annual effective reproductive number would originally be equivalent to 1.65 but finally took on around 0.75 after the emergence of clade 2B-2. The model reported that clade 2B-2 outcompeted for the 2008–2009 influenza season mainly because clade 2C-2 suffered from a reduction of transmission fitness of around 71% on encountering the former.ConclusionsWe conclude that interdisciplinary data-driven mathematical modelling could bring to light the transmission dynamics of the A/H1N1 H275Y strains during the 2007–2009 influenza seasons worldwide and may inspire us to tackle the continually emerging drug-resistant A/H1N1pdm09 strains. Furthermore, we provide a prospective approach through mathematical modelling to solving a seemingly unintelligible problem at the human population level and look forward to its application at molecular level through bridging the resolution capacities of related disciplines.
Highlights
Co-circulation of influenza strains is common to seasonal epidemics and pandemic emergence
Fitting single‐clade influenza season and estimating effective reproductive numbers We first ran the model under the context of the 2007– 2008 influenza season and introduced clade X on April 1, 2007
In terms of the effective reproductive number (Re) estimated, the first parameter set along with the actual data embedded in the model could establish an epidemic 96.83% correlated to the real epidemic of the 2007–2008 influenza season dominated by A/H1N1pdm09: pandemic (A/H1N1) clade 2B-1
Summary
Co-circulation of influenza strains is common to seasonal epidemics and pandemic emergence. Competition was considered involved in the vicissitudes of co-circulating influenza strains but never quantitatively studied at the human population level. The main purpose of the study was to explore the competition dynamics of co-circulating influenza strains in a quantitative way. The results provided insights into the control strategies of influenza pandemics and shed light on the resolution of some enigmas of the seasonal influenza epidemics. One common interest pertinent to seasonal epidemics and pandemic emergence concerns the competition dynamics of co-circulating strains. The transmission dynamics of drug-resistant seasonal A/H1N1 H275Y variants was still mysterious at the human population level
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