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. 2010 Mar 15;5(3):e9565. doi: 10.1371/journal.pone.0009565

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Katriel, Stone.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.

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Assuming , the attack rate (continuous line) is plotted as a function of the initial fraction of susceptibles in the population. An epidemic will not trigger unless the initial susceptibles are greater than , due to herd immunity. The dashed line shows the naive prediction for the attack rate, obtained by extrapolating linearly from the attack rate for , which can be well below the theoretical estimate.

Inline graphic — Assuming , the attack rate (continuous line) is plotted as a function of the initial fraction of susceptibles in the population. An epidemic will not trigger unless the initial susceptibles are greater than , due to herd immunity. The dashed line shows the naive prediction for the attack rate, obtained by extrapolating linearly from the attack rate for , which can be well below the theoretical estimate.