Does the TB vaccine provide protection against SARS-CoV-2?

The BCG vaccine can offer some protection against COVID-19.

The SARS-CoV-2 virus has spread to all parts of the world in the past 12 months. Scientists and health professionals have tried to gather as much information as possible about the virus to aid global efforts to fight COVID-19. One of the few advantages of the virus' s rapid spread is that researchers have been given large sample sizes for observational studies. One such observation in the early months of the pandemic was an obvious correlation between countries vaccinating their populations with the BCG vaccine and improved patient outcomes.

The BCG vaccine has been shown in the past to offer non-specific protection against diseases other than tuberculosis. It is therefore possible that the BCG vaccine could reduce susceptibility to SARS-CoV-2 and / or improve outcomes in people who become infected with the virus. This is the hypothesis that has been put to the test by a new study recently published in the Journal of Clinical Investigation (1).

To test this hypothesis, the researchers looked at a group most affected by SARS-CoV-2 – healthcare workers. At the start of the pandemic, CORALE, the Coronavirus Risk Associations and Longitudinal Evaluation study group, formed a frontline collaboration of clinicians and scientists. This created two cohorts for the purpose of conducting observational research. One of these cohorts included 6,201 frontline healthcare workers. These health care workers have been hired in multiple locations in Los Angeles.

Participants took an electronic survey to collect data on demographics, vaccination history, COVID-19 diagnosis, and experience with COVID-19 symptoms. They also provided a blood sample that tested for the presence of antibodies to the SARS-CoV-2 virus. The sampling was carried out between May 11 and June 18, 2020.

Statistical analysis was then performed to examine the relationship between the BCG vaccine and SARS-CoV-2 infection. The demographic data allowed the researchers to control variables such as age and gender.

Of the original cohort, 1,836 had been vaccinated with the BCG vaccine, 4,275 had not. Overall, 3.5% of the entire cohort tested positive for SARS-CoV-2 antibodies. People who were vaccinated were slightly less likely to report COVID-19-related symptoms in the past six months. Additionally, the likelihood of COVID-19 being diagnosed by either a medical diagnosis or a positive RT-PCR test was significantly lower. This trend was carried over to the antibody seroprevalence results. In the group that received the BCG vaccine, only 2.7% tested positive for SARS-CoV-2 antibodies, while that number rose to 3.8% in the unvaccinated cohort.

The vaccinated cohort was slightly older and contained significantly higher comorbidities such as high blood pressure, cardiovascular diseases and chronic obstructive pulmonary diseases. Nevertheless, the vaccinated cohort performed better in terms of SARS-CoV-2 infection.

The authors also looked at whether a similar pattern is observed when looking at other vaccines. They repeated their analysis with meningococcal, pneumococcal and influenza vaccines. They found that these vaccines did not have the same apparent protective effect as the BCG vaccine.

However, one of the limitations of this study is the fact that the vaccinated cohort contained higher levels of comorbidities. Although this has been reported to reinforce the case for BCG protective effects, the group with more comorbidities may be more cautious in their behavior. It is possible that the lower infection rates in this group are due to behavioral changes rather than a protective BCG effect.

Overall, however, the results strongly suggest that the BCG vaccine provides some protective effect. Although the exact mechanism of this protective effect has not been determined, it has previously been observed in other respiratory diseases. The observational results are compelling and support the wider use of the BCG vaccine, especially in those at greatest risk of serious complications from COVID-19.

Written by

Michael McCarthy

1. Noval Rivas M., Ebinger JE, Wu M., Sun N., Braun J., Sobhani K. et al. BCG vaccination history is linked to decreased SARS-CoV-2 seroprevalence in a diverse cohort of healthcare workers. The Journal of Clinical Investigation. 2020.

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