To the Editors:
Coronavirus disease 2019 (COVID-19) originated in China and has rapidly spread worldwide. Currently, supportive therapy is the most effective treatment. Vaccination is one of the best options for the prevention of infectious diseases. However, a vaccine, as well as a specific proven treatment, remains elusive.
The Bacillus Calmette-Guérin (BCG) vaccine is administered to more than one million children annually in countries with a high prevalence of tuberculosis. Recently, researchers hypothesized that it might also combat COVID-19 because of its broad ability to stimulate the immune system.1 This is based on the fact that countries without universal policies of BCG vaccination (ie, Italy, the Netherlands, and the United States) have been more severely affected compared with countries with universal and long-standing BCG policies.2 Therefore, some researchers are investigating the vaccine’s effectiveness against COVID-19.3
However, it should be emphasized that the causality is not yet proven; there is only one study predicting an association.3 Generally, to clarify the causality between two variables, the Bradford Hill criteria is used.4 To show the causality between the BCG vaccine and the severity of COVID-19, we have to confirm the following Bradford Hill criteria: specificity, temporality, reversibility, and experiment. Until the results of interventional studies are published, we cannot conclusively establish the utility of BCG against COVID-19.
However, many people have misinterpreted this association as causation. This excessive expectation increases individual desire to be vaccinated with BCG. This will cause a big problem for Japanese infants, who, owing to the shortage of BCG, may not get the necessary vaccination. Producing adequate amounts of BCG to meet demands besides that for infant vaccination will take half a year because, at present, only the amount necessary for use in infants is manufactured. Apprehension regarding BCG shortage led the Japanese Society for Vaccinology to officially state that it does not recommend the use of BCG vaccine for the prevention of COVID-19.5 However, under the current Japanese health care system, individuals willing to pay for individual vaccination cannot be prohibited from doing so. Therefore, emphasizing the lack of evidence and the cooperation of Japanese citizens is necessary. If infants in Japan do not receive BCG vaccines, tuberculosis might spread. We must prevent this from happening by publicizing inadequate evidence of causality between the BCG and prevention of the COVID-19. We also need to highlight the concern that a shortage of BCG would exacerbate the tuberculosis crisis among the infants in Japan.
Naoto Kuroda, MD
Department of Pediatrics
Children’s Hospital of Michigan
Wayne State University
Detroit, Michigan
Footnotes
The authors have no funding or conflicts of interest to disclose.
N.K. had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. N.K. contributed to the study concept and design; drafting of the article; Critical revision of the article for important intellectual content.
References
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