New publication on the analysis of the impact of the vaccination campaign on the current H1N1 pandemic

The results of our analysis on the impact of the vaccination campaign on the H1N1 influenza appear in the manuscript

Modeling vaccination campaigns and the Fall/Winter 2009 activity of the new A(H1N1) influenza in the Northern Hemisphere
P Bajardi, C Poletto, D Balcan, H Hu, B Goncalves, JJ Ramasco, D Paolotti, N Perra, M Tizzoni, W Van den Broeck, V Colizza, A Vespignani
Emerging Health Threats Journal 2009, 2:e11.

The paper discusses the effectiveness of the vaccination campaign in mitigating the epidemic in the northern hemisphere, according to the predicted epidemic unfolding. The relative reduction of the epidemic peak activity with respect to the baseline (no-interventions) scenario is measured. Mitigating effects are explored depending on the interplay between the predicted pandemic evolution and the expected delivery and distribution rate of vaccines.

The incidence curves, reported below, show the impact of an incremental vaccination with 1% daily distribution starting on October 15. US and Spain are considered as examples. The model is calibrated using the latest estimates on the transmissibility of the new A(N1H1) influenza, considering as reference the late peak case (the details are reported here). The effect of the vaccination campaign is compared with a combined strategy that includes the systematic treatment of clinical cases with antiviral drugs, where different antiviral distribution rates are considered.

Incidence curves for US and Spain for different intervention scenarios. The gray bar indicates the time period during which the immunization takes effect.

Incidence curves for US and Spain for different intervention scenarios. The gray bar indicates the time period during which the immunization takes effect.

The results show that if additional intervention strategies were not used to delay the time of pandemic peak, vaccination campaigns may not roll out before the pandemic peak is already reached. In the US it is likely that the vaccination campaign will not be able to substantially reduce the epidemic activity, vaccination however will be crucial for the protection of risk groups and healthcare workers. In Europe the activity peak is shifted of a few weeks and the modeling shows that timely vaccination campaigns able to cover 30% of the populations by the second half of November might be effective in mitigating the pandemic. Unfortunately reports of delays in the production and distribution of vaccine have fuelled concern that supplies will arrive too late to make a difference in the number of people that get infected with the new virus. This is again a strong rationale for the prioritized vaccine distribution programs focusing on high-risk groups, healthcare and social infrastructure workers.

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