It is quite interesting to see how the proponents of the hygiene hypothesis are reacting to the Covid-19 pandemic, citing only selected BCG and polio studies and are advising (no disinfectant of course :-) but galectin

The fact that trained immunity can be induced raises the prospect of its exploitation to raise the threshold of resistance to COVID-19 infection … Some studies have already shown that communities that still use Bacillus Calmette–Guérin (BCG) as a vaccine against tuberculosis may have lesser instances of severe COVID-19 infection than those countries that do not use BCG. This notion has been complemented by advocating the use of BCG to vaccinate persons in an attempt to protect them against COVID-19. A recent letter by HIV pioneer Bob Gallo advocated using oral polio vaccine for a similar effect. We consider that administration of galectin molecules, some of which can activate the innate immune system might also represent an approach to reduce the consequences of COVID-19 infection. It is also worth noting that galectin therapy also has the potential to reduce the severity of COVID-19 once infected.

NIH grants EY05093 and AI142862. “Microbes & Infection” has an impact factor 2,3. Published by Institute Pasteur.