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Two academic hospitals in The Netherlands (Nijmegen and Utrecht) just got approval to experiment with using a tuberculosis vaccine (BCG) to try to better protect hospital workers against coronavirus.

I assume that "protect hospital workers" means something like decreasing the severity of the infection.

Apparently the BCG vaccine is known to stimulate the immune system. Given that information, how exactly will it "protect hospital workers"? With or without BCG vaccine, the immune system does not yet have the antibodies against the SARS-CoV-2 (2019-nCoV) coronavirus. So, will the immune system, after BCG vaccination, create more or better antibodies or generate them faster?

https://www.dutchnews.nl/news/2020/03/will-tb-vaccine-help-healthcare-workers-fight-corona-dutch-hospitals-experiment/

Update as of 19 April 2021: "Tuberculosis vaccine does not protect vulnerable elderly against COVID-19" (https://www.umcutrecht.nl/en/about-us/news/details/jan-18-tuberculosis-vaccine-does-not-protect-vulnerable-elderly-against-covid-19).

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  • Interesting study but I think the answer is we're going to have to wait for the results. Like so many corona virus questions, the answer is probably "we just don't know yet."
    – Carey Gregory ♦
    Mar 19, 2020 at 0:16
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    There is some limited evidence of 'off-target' effects of certain vaccines, like the question suggests: by stimulating the immune system in some way; I think it would be possible to write an answer about those effects without any information about covid-19 in particular. Overall this seems to be a bit of a shot in the dark rather than based on something known - the TB vaccine is safe and available, targeted treatments for SARS2 don't exist, why not try?
    – Bryan Krause ♦
    Mar 19, 2020 at 0:35
  • @BryanKrause were you suggesting cross-immunity with "off-target effects"?
    – Bob Ortiz
    Jul 23, 2021 at 9:04
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    @BobOrtiz I'd want to be more careful with that terminology and don't know how for certain how experts use it. My novice assumption is that "cross-immunity" sounds to me like a term I'm more familiar with as "cross-reactivity", when you have specific (antibody-mediated) binding to a different antigen than was initially presented. This is usually a Bad Thing in immunohistochemical assays. What I had in mind here was not that but rather non-specific effects, like changes in the number of circulating immune cells, cytokine levels, etc. This would be consistent with Graham Chiu's answer.
    – Bryan Krause ♦
    Jul 23, 2021 at 10:41

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BCG vaccination appears to enhance the humoral response to general infection. There is said to be also enhanced response so therefore protection against influenza. The trial above is to see if it helps with a response against sars-cov-2.

There is some evidence that BCG vaccination enhances the humoral immune response to other unrelated childhood vaccinations, essentially acting as an adjuvant. Ota et al. reported that infants vaccinated at birth with BCG had, upon vaccination against hepatitis, significantly higher levels of IgG against hepatitis B vaccine antigens. Furthermore, BCG vaccination given at the time of oral polio vaccine boosting improved the antibody response to polio, indicating an effect of BCG at the systemic level (154). An Australian study of 56 BCG-vaccinated and 52 non-BCG vaccinated infants found that BCG vaccination was associated with significantly higher IgG titers against pneumococcal capsular polysaccharide antigens, H.influenzae type b polysaccharide and tetanus toxoid following routine immunisations later in infancy

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6579862/

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