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. 2021 Feb 18;8:637580. doi: 10.3389/fvets.2021.637580

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Copyright © 2021 Srinivasan, Conlan, Easterling, Herrera, Dandapat, Veerasami, Ameni, Jindal, Raj, Wood, Juleff, Bakker, Vordermeier and Kapur.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Measures of vaccine-induced protection. (A) BCG vaccine confers a spectrum of protection ranging from complete (for a limited time period in certain population) to none. While completely protected individuals are immune, and unprotected ones succumb to infection and become heavily diseased, BCG can also be partially protective by reducing risk of disease transmission to unvaccinated individuals. (B) The green herd is partially vaccinated and the blue herd is unvaccinated. “Direct protection” is the reduction in susceptibility of vaccinated animals (as measured by ε_s). “Indirect protection” is a reduction in transmission due to any reduction in infectiousness of vaccinated individuals that become infected (as measured by ε_I) in addition to the reduction in transmission from herd immunity effects. “Total” protection is the risk of infection in vaccinated animals compared to that of unvaccinated animals. “Overall protection” is the reduction in rate of transmission in a population with vaccination program compared to that in a population with no vaccination program. This stems from both vaccinated and unvaccinated individuals and is used to evaluate the impact of a vaccination program at the population level. (B) Is adapted from Halloran et al. (43).