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BCG vaccination history associates with decreased SARS-CoV-2 seroprevalence across a diverse cohort of healthcare workers

Our take —

This study examined the relationship between history of BCG vaccination and SARS-CoV-2 infection prevalence among a group of 6,670 health care workers in Los Angeles County, US. Findings suggest that the BCG vaccine, which was originally developed to protect against tuberculosis, can reduce the risk of developing COVID-19 in individuals who were vaccinated in the past. Clinical trials are currently underway to examine if prospective BCG vaccination can be protective against COVID-19.

Study design

Retrospective Cohort

Study population and setting

The study included 6,679 health care workers in Cedars-Sinai Health System network around the Los Angeles County area. The correlation between COVID-19 infection and the history of BCG vaccination was assessed. SARS-CoV-2 infection was determined by measuring IgG levels in over 92% of the participants and by self-reporting of COVID-19-related symptoms in the remaining subjects. History of vaccination against meningococcal, influenza, and pneumococcal vaccination was used as control. The authors also compared the prevalence of four common preexisting conditions: hypertension, diabetes mellitus, cardiovascular diseases, and chronic obstructive pulmonary disease among the participants in the study.

Summary of Main Findings

Less than one third (30%) of the participants were BCG vaccinated with an average age of 43 years compared to 40 years in the non-vaccinated group. The rate of self-reported COVID-19 diagnosis and RT-PCR positivity were 1.9% and 1% in the BCG vaccinated group compared to 2.9% and 1.7% in the control group, respectively. In addition, anti-SARS-CoV-2 IgG antibodies were detected in 2.7% in BCG vaccinated participants and in 3.8% of the control group. Participants in the BCG vaccinated group reported higher rates of all these four co-morbidities compared to those in the control group, excluding the possibility that the differences in COVID-19 incidence between both groups reflect variations in the prevalence of preexisting comorbidities.

Study Strengths

The current study has the advantage of including a relatively large number of participants. As the participants in this study were health care workers, the self-reported medical history is more reliable compared to similar studies in which participants were recruited from the general population. In addition, the high rate of seropositivity in this cohort allowed robust testing of the hypothesis.


Most of the limitations are related to the nature of retrospective studies including the reliability of the self-reporting medical history. In addition, there were some statistically significant and potentially confounding differences between the BCG vaccinated and not-vaccinated groups including age, sex and ethnicity. The study did not include the timeline of BCG vaccination in the participants. Finally, the mechanism of how BCG vaccination could reduce viral infection is unknown.

Value added

This study showed that in individuals who have received the safe and inexpensive BCG vaccine in the past may have a reduced risk of SARS-COV-2 infection.

This review was posted on: 3 January 2021