Abstract
The unfolding of pandemic influenza A(H1N1) for Fall 2009 in the Northern Hemisphere is still uncertain. Plans for vaccination campaigns and vaccine trials are underway, with the first batches expected to be available early October. Several studies point to the possibility of an anticipated pandemic peak that could undermine the effectiveness of vaccination strategies. Here, we use a structured global epidemic and mobility metapopulation model to assess the effectiveness of massive vaccination campaigns for the Fall/Winter 2009. Mitigation effects are explored depending on the interplay between the predicted pandemic evolution and the expected delivery of vaccines. The model is calibrated using recent estimates on the transmissibility of the new A(H1N1) influenza. Results show that if additional intervention strategies were not used to delay the time of pandemic peak, vaccination may not be able to considerably reduce the cumulative number of cases, even when the mass vaccination campaign is started as early as mid-October. Prioritized vaccination would be crucial in slowing down the pandemic evolution and reducing its burden.
Highlights
IntroductionWith decreasing trends for pandemic H1N1 cases reported in most of the Southern Hemisphere countries, the concerns regarding the epidemic evolution are focusing on the influenza activity during Fall 2009 in the Northern Hemisphere.[1,2,3] The future unfolding of a pandemic is dominated by a large degree of uncertainty, several studies and technical reports recently outlined a likely course of the pandemic in the few months, identifying plausible scenarios and quantifying the expected impact on the population.[4,5,6,7,8] The modeling approaches in these studies are characterized by the likelihood of an early epidemic activity in the Northern Hemisphere, with the peak expected to occur in October/November
Vaccine delivery is scheduled to start in early or mid-October[10] in several countries, but the expected timing of the pandemic influenza activity predicted to peak in October/November puts at risk the effectiveness of mass vaccination as a control strategy
The benchmark to evaluate the effect of mass vaccination campaigns is the no intervention scenario that is predicted to reach the activity peak for example, in the United States between the beginning of October and the beginning of November
Summary
With decreasing trends for pandemic H1N1 cases reported in most of the Southern Hemisphere countries, the concerns regarding the epidemic evolution are focusing on the influenza activity during Fall 2009 in the Northern Hemisphere.[1,2,3] The future unfolding of a pandemic is dominated by a large degree of uncertainty, several studies and technical reports recently outlined a likely course of the pandemic in the few months, identifying plausible scenarios and quantifying the expected impact on the population.[4,5,6,7,8] The modeling approaches in these studies are characterized by the likelihood of an early epidemic activity in the Northern Hemisphere, with the peak expected to occur in October/November. As an effective line of defense against influenza epidemics, most of the countries are planning the vaccination of a large fraction of the population.[9] Started after the virus identification at the end. Of April 2009, the vaccine development and production is well under way and recently received the approval by the US Food and Drugs Administration.[10] Vaccine delivery is scheduled to start in early or mid-October[10] in several countries, but the expected timing of the pandemic influenza activity predicted to peak in October/November puts at risk the effectiveness of mass vaccination as a control strategy
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