BCG vaccine-induced trained immunity and COVID-19: Protective or bystander?

Gopala Koneru, Gaber El Saber Batiha, Abdelazeem M. Algammal, Mahmoud Mabrok, Sara Magdy, Shrouk Sayed, Mai E. AbuElmagd, Reham Elnemr, Mahmoud M. Saad, Noura H. Abd Ellah, Amal Hosni, Khalid Muhammad, Helal F. Hetta

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


In late 2019, a new virulent coronavirus (CoV) emerged in Wuhan, China and was named as severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). This virus spread rapidly, causing the coronavirus disease-2019 (COVID-19) pandemic. Bacillus Calmette-Guérin (BCG) is a live attenuated tuberculosis (TB) vaccine, associated with induction of non-specific cross-protection against unrelated infections. This protection is a memory-like response in innate immune cells (trained immunity), which is caused by epigenetic reprogramming via histone modification in the regulatory elements of specific genes in monocytes. COVID-19 related epidemiological studies showed an inverse relation- ship between national BCG vaccination policies and COVID-19 incidence and death, suggesting that BCG may induce trained immunity that could confer some protection against SARS-CoV-2. As this pandemic has put most of Earth’s population under quarantine, repurposing of the old, well-characterized BCG may ensure some protection against COVID-19. This review focuses on BCG-related cross-protection and acquisition of trained immunity, as well as the correlation between BCG vaccination and COVID-19 incidence and mortality.

Original languageEnglish
Pages (from-to)1169-1184
Number of pages16
JournalInfection and Drug Resistance
Publication statusPublished - 2021


  • BCG vaccine
  • Coronavirus
  • Covid-19
  • Trained immunity
  • Tuberculosis

ASJC Scopus subject areas

  • Pharmacology
  • Infectious Diseases
  • Pharmacology (medical)


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