The Transmissibility and Control of
Pandemic Influenza A (H1N1) Virus
Jonathan D. Sugimoto,
M. Elizabeth Halloran,
Nicole E. Basta,
Dennis L. Chao,
Ira M. Longini Jr.
Pandemic influenza A (H1N1) 2009 (pandemic H1N1) is spreading throughout the planet. It has
become the dominant strain in the Southern Hemisphere, where the influenza season has now ended.
Here, on the basis of reported case clusters in the United States, we estimated the household secondary
attack rate for pandemic H1N1 to be 27.3% [95% confidence interval (CI) from 12.2% to 50.5%].
From a school outbreak, we estimated that a typical schoolchild infects 2.4 (95% CI from 1.8 to 3.2)
other children within the school. We estimated the basic reproductive number,
1.3 to 1.7 and the generation interval to range from 2.6 to 3.2 days. We used a simulation model to
evaluate the effectiveness of vaccination strategies in the United States for fall 2009. If a vaccine were
available soon enough, vaccination of children, followed by adults, reaching 70% overall coverage,
in addition to high-risk and essential workforce groups, could mitigate a severe epidemic.
andemic H1N1, which first emerged in
Mexico in April 2009, had spread world-
wide, resulting in more than 130,000
laboratory-confirmed cases and 800 deaths in
over 100 countries, by mid-July (
). The global
distribution of this novel strain prompted the
World Health Organization to declare the first
influenza pandemic of the 21st century in June
). Initially, most cases were clustered in