Giuseppe
Emeritus
[Source: ScienceDirect, Epidemics, full text: (LINK). Abstract, edited.]
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Critical immune and vaccination thresholds for determining multiple influenza epidemic waves
Publication year: 2011
Source: Epidemics, Available online 7 December 2011
Laura Matrajt, Ira M. Longini
Previous influenza pandemics (1918, 1957, and 1968) have all had multiple waves. The 2009 pandemic influenza A(H1N1) (pandemic H1N1) started in April 2009 and was followed, in the United States (US) and temperate Northern Hemisphere, by a second wave during the fall of 2009. The ratio of susceptible and immune individuals in a population at the end of a wave determines the potential and magnitude of a subsequent wave. As influenza vaccines are not completely protective, there was a combined immunity in the population at the beginning of 2010 (due to vaccination and due to previous natural infection), and it was uncertain if this mixture of herd immunity was enough to prevent a third wave of pandemic influenza during the winter of 2010. Motivated by this problem, we developed a mathematical deterministic two-group epidemic model with vaccination and calibrated it for the 2009 pandemic H1N1. Then, applying methods from mathematical epidemiology we developed a scheme that allowed us to determine critical thresholds for vaccine-induced and natural immunity that would prevent the spread of influenza. Finally, we estimated the level of combined immunity in the US during winter 2010. Our results suggest that a third wave was unlikely if the basic reproduction numberR0were below 1.6, plausible if the originalR0was 1.6, and likely if the originalR0was 1.8 or higher. Given that the estimates for the basic reproduction number for pandemic influenza place it in the range between 1.4 and 1.6 (Bacaer and Ait Dads, 2011; Fraser et al., 2009; Munayco et al., 2009; Pourbohloul et al., 2009; Tuite et al., 2010; White et al., 2009; Yang et al., 2009), our approach accurately predicted the absence of a third wave of influenza in the US during the winter of 2010.We also used this scheme to accurately predict the second wave of pandemic influenza in London and the West Midlands, UK during the fall of 2009.
Highlights
► In the past century, there were three major influenza pandemics (1918, 1957, and 1968) and they all have had multiple waves. ► At the end of the second wave of the current H1N1 epidemic, a fraction of the population has vaccine-induced immunity and some other fraction has natural-induced immunity. ► Will this ?mixture? of immunity be enough to prevent a third wave? ► A third wave of pandemic H1N1 in the US was unlikely.
-Publication year: 2011
Source: Epidemics, Available online 7 December 2011
Laura Matrajt, Ira M. Longini
Previous influenza pandemics (1918, 1957, and 1968) have all had multiple waves. The 2009 pandemic influenza A(H1N1) (pandemic H1N1) started in April 2009 and was followed, in the United States (US) and temperate Northern Hemisphere, by a second wave during the fall of 2009. The ratio of susceptible and immune individuals in a population at the end of a wave determines the potential and magnitude of a subsequent wave. As influenza vaccines are not completely protective, there was a combined immunity in the population at the beginning of 2010 (due to vaccination and due to previous natural infection), and it was uncertain if this mixture of herd immunity was enough to prevent a third wave of pandemic influenza during the winter of 2010. Motivated by this problem, we developed a mathematical deterministic two-group epidemic model with vaccination and calibrated it for the 2009 pandemic H1N1. Then, applying methods from mathematical epidemiology we developed a scheme that allowed us to determine critical thresholds for vaccine-induced and natural immunity that would prevent the spread of influenza. Finally, we estimated the level of combined immunity in the US during winter 2010. Our results suggest that a third wave was unlikely if the basic reproduction numberR0were below 1.6, plausible if the originalR0was 1.6, and likely if the originalR0was 1.8 or higher. Given that the estimates for the basic reproduction number for pandemic influenza place it in the range between 1.4 and 1.6 (Bacaer and Ait Dads, 2011; Fraser et al., 2009; Munayco et al., 2009; Pourbohloul et al., 2009; Tuite et al., 2010; White et al., 2009; Yang et al., 2009), our approach accurately predicted the absence of a third wave of influenza in the US during the winter of 2010.We also used this scheme to accurately predict the second wave of pandemic influenza in London and the West Midlands, UK during the fall of 2009.
Highlights
► In the past century, there were three major influenza pandemics (1918, 1957, and 1968) and they all have had multiple waves. ► At the end of the second wave of the current H1N1 epidemic, a fraction of the population has vaccine-induced immunity and some other fraction has natural-induced immunity. ► Will this ?mixture? of immunity be enough to prevent a third wave? ► A third wave of pandemic H1N1 in the US was unlikely.
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