key: cord-1046182-pw4v8l6d
authors: Patella, Vincenzo; Delfino, Gabriele; Bruzzese, Dario; Giuliano, Ada; Sanduzzi, Alessandro
title: The bacillus Calmette–Guérin vaccination allows the innate immune system to provide protection from severe COVID-19 infection
date: 2020-10-13
journal: Proc Natl Acad Sci U S A
DOI: 10.1073/pnas.2015234117
sha: ee50121ca67bd330d787f82443d540356132f229
doc_id: 1046182
cord_uid: pw4v8l6d

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systems and greater population density, where the COVID-19 epidemic presented a multilevel emergency (health, social, and political), not all deaths were adequately assessed for the cause. It is therefore probable that several COVID-19 deaths could have not been counted and therefore not reported, resulting in an underestimation of mortality rate. This phenomenon is likely to be more frequent in poorer countries with a lower Human Development Index (HDI). Probably this could partly explain why lower mortality rates have been observed in countries with lower HDI. What happened in China is also significant: The local authorities revised upward the data on the number of deaths. The explanation of high mortality in France and the United Kingdom is not very convincing, despite the bacillus Calmette-Guérin vaccination; the authors justify the ineffectiveness of the trained immunity with the age of administration of bacillus Calmette-Guérin vaccine (in many cases, it is not carried out during early childhood, but in the second and third stages of childhood). According to mechanisms of trained immunity, it is conceivable that this can be sustained even in the older child, where there is an innate immune system preponderance compared to adaptive immunity that is still incomplete. This is also motivated by regression of time, which does not begin before puberty.

Furthermore, the indiscriminate use of bacillus Calmette-Guérin vaccine could present a serious risk of depletion of the stocks currently available globally, with the consequent lack of a preventive measure versus tuberculosis. As pointed out by the authors, the recommendations of the World Health Organization (6) reiterate that it is necessary to await the results of ongoing clinical trials (7, 8) . 

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