Emily MacLeanPhD candidate, McGill University
- McGill University
About Emily MacLean
Channels contributed to:Journal Club World Tuberculosis Day 2017 After the Paper Coronaviruses: Past, Present and Future
Unlike Jane I found this blog to be very well written and very much on topic. I think the two studies linking BCG to COVID19 infection or mortality rates should have looked at some obvious confoundig factors.
Not perfect but a start...
Thanks for sharing your piece. Will read with interest
This post nicely summarizes the weaknesses of ecological correlation studies, and to that I'd add only one point: it may suffer from "presentism." If one is interested in mortality of the elderly, particularly males, immunization policies in the 1940s-1960s may be critical. At age 80, I remember being immunized in the US against TB (leaves a big scar on shoulder!), and receiving booster shots in the military in the 1950s. I've no idea of the timetable for cessation of immunization thereafter.
As to biological plausibility, the first internet posting I saw re BCG (https://www.sciencemag.org/news/2020/03/can-century-old-tb-vaccine-steel-immune-system-against-new-coronavirus?utm_source=Global+Health+NOW+Main+List&utm_campaign=18482039f6-EMAIL_CAMPAIGN_2020_03_23_12_56&utm_medium=email&utm_term=0_8d0d062dbd-18482039f6-871647 ) emphasized that BCG might also boost INNATE immunity in addition to inducing specific cellular-mediated immunity, which is what would boost covid9 resistance. Apparently innate immunity has recently been found to have some memory, although whether extending beyond the persistence of BCG organisms in the skin was obscure.
I consequently wondered whether a stiff tuberculin injection in those elderly vaccinated when young against TB might incidentally boost innate immunity and give some protection against current viral infections.
Take this with a grain of salt. The writer is long retired, never worked on infectious diseases as part of his epidemiological research, and is working from memory!
Thanks for the comments! It definitely now does seem like there is an innate component to BCG-mediated immunity. And the recent studies about revaccinating young adults with BCG to boost anti TB immunity are v intriguing. Our point I guess is that from this ecological study alone, it is not possible to know whether it would extend to one particular other disease. Maybe it does! Maybe it doesn't! But we'll know with further research !