The possible puzzles of BCG vaccine in protection against COVID-19 infection

Abstract Background The paper aimed to analyze and evaluate the present literature data on clinical effectiveness of using bacillus Calmette–Guérin (BCG) vaccine in protecting against novel coronavirus disease 2019 (COVID-19). Main body Several have shown a relationship between vaccinated population with severity mortality rate from However, linkage BCG COVID-19 infection morbidity is still ambiguous. has been protected previously many other respiratory viral infections. efficacy protection depends various factors including social, economic, cultural norms, mitigation efforts, health infrastructure, demographic differences countries. Conclusion Thus, analyses show noticed difference countries that follow national vaccination programs than do not such (Italy, Netherlands, USA). there are any recommendations for severe cases COVID-19. maybe age, immune state patient, level coverage. possible reason trained immunity both diseases.