Abstract
The Bacillus Calmette–Guerin (BCG) vaccine provides protection against tuberculosis (TB), and is thought to provide protection against non-TB infectious diseases. BCG vaccination has recently been proposed as a strategy to prevent infection with SARS-CoV-2 (CoV-2) to combat the COVID-19 outbreak, supported by its potential to boost innate immunity and initial epidemiological analyses which observed reduced severity of COVID-19 in countries with universal BCG vaccination policies. Seventeen clinical trials are currently registered to inform on the benefits of BCG vaccinations upon exposure to CoV-2. Numerous epidemiological analyses showed a correlation between incidence of COVID-19 and BCG vaccination policies. These studies were not systematically corrected for confounding variables. We observed that after correction for confounding variables, most notably testing rates, there was no association between BCG vaccination policy and COVD-19 spread rate or percent mortality. Moreover, we found variables describing co-morbidities, including cardiovascular death rate and smoking prevalence, were significantly associated COVID-19 spread rate and percent mortality, respectively. While reporting biases may confound our observations, our epidemiological findings do not provide evidence to correlate overall BCG vaccination policy with the spread of CoV-2 and its associated mortality.
Highlights
The Bacillus Calmette–Guerin (BCG) vaccine provides protection against tuberculosis (TB), and is thought to provide protection against non-TB infectious diseases
Since the early 1920s, the use of the Bacillus Calmette–Guerin (BCG) vaccine has been implemented in several countries to prevent tuberculosis (TB), a disease caused by Mycobacterium tuberculosis
SARS-CoV-2 testing rates influence the observed benefit of BCG vaccination policy. (a) Correlation graph of total COVID-19 spread rate and tests per thousand inhabitants
Summary
The Bacillus Calmette–Guerin (BCG) vaccine provides protection against tuberculosis (TB), and is thought to provide protection against non-TB infectious diseases. BCG vaccination has recently been proposed as a strategy to prevent infection with SARS-CoV-2 (CoV-2) to combat the COVID-19 outbreak, supported by its potential to boost innate immunity and initial epidemiological analyses which observed reduced severity of COVID-19 in countries with universal BCG vaccination policies. Numerous epidemiological analyses showed a correlation between incidence of COVID-19 and BCG vaccination policies These studies were not systematically corrected for confounding variables. In most countries with high TB incidence, a universal BCG vaccination policy has been implemented, where children receive the BCG vaccine in early infancy. The BCG vaccine may offer protection for as long as 30–40 years post vaccination (as previously reported in N orway4), and possibly as long as 50–60 years, as reported in American Indians and Alaska Natives that participated in a BCG vaccine trial[5] These studies show a reduction in long-lasting protection which is in line with studies showing that the protective effect of the BCG vaccine is decreased over time (reviewed in6). Efficacy of BCG Vaccination in the Prevention of COVID19 Via the Strengthening of Innate Immunity in Health Care Workers (COVID-BCG)
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