Debate on Bacille Calmette-Guérin vaccination against COVID-19: Is it worth performing clinical trials?

Luca, 2013, History of BCG vaccine, Maedica, 8, 53 Sánchez-Ramón, 2018, Trained immunity-based vaccines: a new paradigm for the development of broad-spectrum anti-infectious formulations, Front. Immunol., 9, 2936, 10.3389/fimmu.2018.02936 Netea, 2020, Trained immunity: a tool for reducing susceptibility to and the severity of SARS-CoV-2 infection, Cell, 181, 969, 10.1016/j.cell.2020.04.042 Kleinnijenhuis, 2014, Long-lasting effects of BCG vaccination on both heterologous Th1/Th17 responses and innate trained immunity, J. Innate Immun., 6, 152, 10.1159/000355628 Curtis, 2020, Considering BCG vaccination to reduce the impact of COVID-19, Lancet, 395, 1545, 10.1016/S0140-6736(20)31025-4 Wang, 2020, Remdesivir in adults with severe COVID-19: a randomised, double-blind, placebo-controlled, multicentre trial, Lancet (London, England), 395, 1569, 10.1016/S0140-6736(20)31022-9 Hegarty, 2020, COVID-19 and Bacillus Calmette-Guérin: what is the link?, Eur. Urol. Oncol., 3, 259, 10.1016/j.euo.2020.04.001 Hamiel, 2020, SARS-CoV-2 rates in bcg-vaccinated and unvaccinated young adults, JAMA, 10.1001/jama.2020.8189 Mahase, 2020, Covid-19: what treatments are being investigated?, BMJ, 368, m1252, 10.1136/bmj.m1252 Hensel, 2020, Exercising caution in correlating COVID-19 incidence and mortality rates with BCG vaccination policies due to variable rates of SARS CoV-2 testing, Medrxiv Miyasaka, 2020, Is BCG vaccination causally related to reduced COVID-19 mortality?, EMBO Mol. Med., 10.15252/emmm.202012661 Moorlag, 2019, Non-specific effects of BCG vaccine on viral infections, Clin. Microbiol. Infect., 25, 1473, 10.1016/j.cmi.2019.04.020 Wardhana, 2011, The efficacy of Bacillus Calmette-Guerin vaccinations for the prevention of acute upper respiratory tract infection in the elderly, Acta Med. Indonesiana, 43, 185 Leentjens, 2015, BCG vaccination enhances the immunogenicity of subsequent influenza vaccination in healthy volunteers: a randomized, placebo-controlled pilot study, J. Infect. Dis., 212, 1930, 10.1093/infdis/jiv332 Arts, 2018, BCG vaccination protects against experimental viral infection in humans through the induction of cytokines associated with trained immunity, Cell Host Microbe, 23, 89, 10.1016/j.chom.2017.12.010 Tarancón, 2020, New live attenuated tuberculosis vaccine MTBVAC induces trained immunity and confers protection against experimental lethal pneumonia, PLoS Pathog., 16, 10.1371/journal.ppat.1008404