To evaluate the impact of mass vaccination with adjuvanted vaccines (eventually 40% population coverage) and antivirals during the 2009 influenza pandemic in Norway, we fitted an age-structured SEIR model using data on vaccinations and sales of antivirals in 2009/10 in Norway to Norwegian ILI surveillance data from 5 October 2009 to 4 January 2010. We estimate a clinical attack rate of approximately 30% (28.7-29.8%), with highest disease rates among children 0-14 years (43-44%). Vaccination started in week 43 and came too late to have a strong influence on the pandemic in Norway. Our results indicate that the countermeasures prevented approximately 11-12% of potential cases relative to an unmitigated pandemic. Vaccination was found responsible for roughly 3 in 4 of the avoided infections. An estimated 50% reduction in the clinical attack rate would have resulted from vaccination alone, had the campaign started 6 weeks earlier. Had vaccination been prioritized for children first, the intervention should have commenced approximately 5 weeks earlier in order to achieve the same 50% reduction. In comparison, we estimate that a non-adjuvanted vaccination program should have started 8 weeks earlier to lower the clinical attack rate by 50%. In conclusion, vaccination timing was a critical factor in relation to the spread of the 2009 A(H1N1) influenza. Our results also corroborate the central role of children for the transmission of A(H1N1) pandemic influenza.
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Cites: Am J Epidemiol. 2004 Apr 1;159(7):623-3315033640
Cites: BMJ. 2011;343:d540821903689
Cites: Am J Epidemiol. 2007 Jan 15;165(2):212-2117088311
Cites: Am J Epidemiol. 2008 Apr 1;167(7):775-8518230677
Cites: Science. 2009 Jun 19;324(5934):1557-6119433588
Cites: Euro Surveill. 2009 Jul 9;14(27). pii: 1926419589329
Cites: Euro Surveill. 2009;14(40). pii: 1935419822124
Cites: Wkly Epidemiol Rec. 2009 Nov 13;84(46):481-419928298
Cites: Euro Surveill. 2010 Feb 4;15(5). pii: 1947820144443