Association of BCG with low COVID-19 mortality

The association between BCG (Bacillus Calmette-Guérin) vaccination and its beneficial effect on COVID-19 infection / mortality was challenged by expert assessments of Diamond Princess cruise ship data. At the same time, previously reported cross-border differences were shown to be flawed, and new reports medRxiv Investigation.

The global pandemic of coronavirus disease (COVID-19) caused by severe acute respiratory coronavirus 2 (SARS-CoV-2) represents an international public health crisis. With no vaccine or effective cure yet, the scientific community is exploring different options to reduce the burden of infection.

Recently, several author groups have proposed the hypothesis that BCG vaccination reduces both COVID-19 morbidity and mortality. The correlation between national BCG vaccination policy and infection rates probably supported this hypothesis.

It was hypothesized that the BCG vaccine does not specifically prevent tuberculosis, influenza, or COVID-19, but that it has a “harmonizing effect” that actually directs the immune system to respond.

However, the hypothesis that BCG vaccination reduces SARS-CoV-2 infectivity and COVID-19 mortality is interesting, but a recent study written by Dr. Masakazu Asahara of the Faculty of Liberal Arts and Sciences Disproved The College of Nissi.

Novel coronavirus SARS-CoV-2 transmission electron micrograph of SARS-CoV-2 virus particles isolated from a patient. Color-enhanced image captured at the NIAID Integrated Research Facility (IRF) in Fort Detrick, MD. Credit: NIAID

Local and international comparison

In order to examine the hypothesis in more detail, this paper (Available on preprint server medRxivWe have pursued statistical analysis of publicly available data using several different approaches. The first step was to compare individual morbidity and mortality on the international cruise ship Diamond Princess, which carries around 3,700 passengers.

The majority of patients on board were infected before they were aware of the spread of SARS-CoV-2 on board. That is, you can exclude cultural specificities of different countries (such as the habit of wearing masks) or national policies (for example, the “cluster buster” policy enacted in Japan), while at the same time the same virus strain is involved in the outbreak. I found out that .

The next step was to compare the number of deaths for each country and the maximum daily increase in total deaths for each country. A general linear model was used to assess the effects of BCG vaccination and the timing of COVID-19 invasion into countries and regions.

No correlation with COVID-19

As a result, there was no significant difference between the infection rates and mortality rates of Japanese and other nationalities, and between BCG and non-BCG duty countries on Diamond Princess cruise ships.

Moreover, after compensating for SARS-CoV-2 arrival times in various countries, the previously disclosed effects of BCG vaccination on lowering total mortality are virtually gone. This is due to the fact that countries that are not vaccinated against BCG are concentrated in Western Europe near the epicenter of COVID-19.

Finally, the maximum daily growth rate of deaths in each country did not show a significant difference between BCG vaccination policies. In fact, Japan had a weak correlation, which could have been influenced by sample size, outliers, and significant regional differences.

The results show that even with BCG vaccination, its beneficial effects can be masked by a myriad of other factors. Therefore, the possible impact may be quite small. In fact, almost every citizen in Japan is vaccinated, but the number of cases of COVID-19 is constantly increasing.

The World Health Organization warns that such ecological studies are always subject to significant bias due to many confounding factors. This includes differences in national demographics and disease burden, pandemic stages in different countries, and test rates.

“There can be many hypotheses that explain the morbidity, mortality, and differences in COVID-19 and how they increase in different countries,” Ashara explains. “A simple comparison between nations may address these issues / hypotheses.”

Notes

The link between BCG and COVID-19 has not been proven, but many media and social networks have reported hypotheses, and people have gradually come to regard it as a fact (especially the BCG vaccine program In active countries).

“The hypothesis that BCG vaccination reduces COVID-19 infection and mortality is appealing,” said Dr Ashara in the study. “But many other possibilities could explain the observed pattern, so previous international comparative reports may not prove the hypothesis,” he adds.

In any case, ongoing clinical research will give the final answer to this question. Until then, the research community needs to be careful when reporting patterns that appear in statistical data and do not cause more harm than harm when spreading optimistic conclusions from unproven theories. Warns Dr. Ashara.

Despite the lack of evidence, WHO has not yet recommended BCG vaccination for the prevention of COVID-19. Nevertheless, further research progress is closely monitored and neonatal BCG vaccination in countries with high incidence of tuberculosis is still recommended.