BCG vaccination induced protection from COVID-19

Area of Science:

• Immunology
• Infectious Diseases
• Vaccinology

Background:

• The global search for a SARS-CoV-2 vaccine faces challenges, prompting investigation into repurposing existing vaccines.
• Countries with routine Bacillus Calmette-Guérin (BCG) vaccination programs report lower COVID-19 incidence, suggesting a potential protective role.
• Tuberculosis-endemic nations, like India, exhibit lower COVID-19 mortality and severity despite population density, hinting at immune-protective factors.

Purpose of the Study:

• To explore the potential protective mechanisms of BCG vaccination against COVID-19.
• To investigate the role of non-specific effects (NSEs) of BCG in trained immunity and protection against viral infections.
• To examine factors contributing to lower COVID-19 severity in BCG-vaccinated populations and TB-endemic regions.

Main Methods:

• Observational analysis of COVID-19 incidence and mortality rates in countries with and without routine BCG vaccination programs.
• Review of existing literature on BCG's non-specific effects (NSEs), trained immunity, and heterologous lymphocyte activation.
• Comparative analysis of COVID-19 outcomes in TB-endemic versus non-endemic regions.

Main Results:

• BCG vaccination is associated with reduced COVID-19 incidence in countries where it is routinely administered.
• Evidence suggests BCG induces immunological memory and trained immunity, potentially offering cross-protection against other infections, including viral ones.
• While BCG at birth may not protect adults, other factors like environmental Mycobacteria in TB-endemic areas might contribute to reduced COVID-19 severity.

Conclusions:

• BCG vaccination may confer partial protection against COVID-19 severity through its non-specific immune-stimulating effects.
• The concept of trained immunity induced by BCG could be relevant for combating SARS-CoV-2.
• Further research is warranted to understand the full potential of BCG and environmental Mycobacteria in mitigating COVID-19 outcomes, especially in high-prevalence regions.