Tuberculosis vaccine BCG: the magical effect of the old vaccine in the fight against the COVID-19 pandemic.

Bacillus Calmette-Guérin (BCG) is a live attenuated M. bovis vaccine that was developed about 100 years ago by Albert Calmette and Camille Guérin. Many countries have been using the vaccine for decades against tuberculosis (TB). The World Health Organization (WHO) recommends a single dose of BCG for infants in TB endemic as well as leprosy high risk countries, and globally almost 130 million infants are vaccinated yearly. The role of BCG is well known in reducing neonatal and childhood death rates. Epidemiological and retrospective cross-sectional studies demonstrated that the BCG vaccination protects the children against respiratory tract infections and lowers the risk of malaria in children. In addition, BCG enhances IFN-γ and IL-10 levels, thus providing immunity against respiratory tract infection even in elderly people. The BCG is also known to provide nonspecific innate immunity against viruses and parasites, through an innate immune mechanism termed 'trained immunity' and is defined as the immunological recall of the innate immune system by epigenetic reprogramming. Based on these studies it is suggested that the BCG has the potential to act as a protective agent against COVID-19. Further proven safety records of BCG in humans, its adjuvant activity and low-cost manufacturing make it an attractive option to stop the pandemic and reduce the COVID-19 related mortality. In this review we discuss the heterologous effects of BCG, induction of trained immunity and its implication in development of a potential vaccine against COVID-19 pandemic.

Is the tuberculosis vaccine BCG an alternative weapon for developing countries to defeat COVID-19?

BACKGROUD: Coronavirus disease (COVID-19) is a new respiratory infectious disease, and there is no vaccine currently. Previous studies have found that BCG vaccination can provide extensive protection against respiratory infectious diseases. METHODS: Herein, we obtained the latest data from the World Health Organization (WHO) as of August 12, 2020, and determined the relationship between three parameters (including the BCG vaccination coverage, human development index (HDI), and transmission classifications) and the incidence rate and mortality of COVID-19. RESULTS: The results showed that the morbidity and mortality of COVID-19 in countries with BCG vaccination recommendation were significantly lower than these in countries without BCG vaccination recommendation, and countries with lower HDI have lower morbidity and mortality. In addition, we also found that the mode of virus transmission is also related to the morbidity and mortality of COVID-19. CONCLUSIONS: Although our data supports the hypothesis that BCG vaccination is beneficial in reducing the morbidity and mortality of COVID-19, the data supporting this result may be inaccurate due to many confounders such as PCR testing rate, population characteristics, and protection strategies, the reliability of this result still needs to be verified by clinical trials.