Do BCG Vaccinated Populations Have Non-Specific Immunity for COVID 19? A Review of the Literature

The paper presents and summarizes the findings of recent research studies that investigate the influence of Bacille Calmette Guérin (BCG) vaccine on the COVID-19-related cases and deaths. This paper focuses on the evolution of the research findings relating to COVID-19 disease pattern and that claimed relationship between mandatory BCG policy and COVID-19 since the beginning of the COVID-19 pandemic. We analyze 47 peer- and non-peer-reviewed publications studying the impact of BCG vaccination on the infection rates and death rates of COVID-19. We divide the review of published literature in line with evolution phases of the COVID-19 disease which are linked to time since the initial phase and focus on the disease spread. In the analysis we distinguish between three major phases of COVID-19 evolution, according to which we group the published research papers: 1. Initial Phase (February to April 2020), 2. Mid-Phase (May to July 2020), and 3. Maturity Phase (August 2020 and later). While in the initial phase a very high proportion of studies found support for the hypothesis that BCG vaccinated populations show slower spread of COVID-19 pointing to some non-specific immunity related advantage to these populations, over the mid-phase and maturity phase a larger proportion of studies find weak to no relationship.