@leggi, thanks, I think the key thing here is that BCG isn't used to protect you against TB here, but broadly boost your immune system. I found a bunch of papers on this (admittedly, many about youth, but also some on the elderly getting BCG):
What I want to call out in the context of the elderly:
The efficacy of Bacillus Calmette-Guerin vaccinations for the prevention of acute upper respiratory tract infection in the elderly.
AIM: to study the efficacy of BCG vaccinations, once a month for 3 consecutive months, in elderly on the prevention of acute upper respiratory tract infection (AURTI), interferon - gamma (IFN-γ) and interleukin (IL)-10 level in the BCG and placebo group and their comparison in the period of the study.
CONCLUSION: BCG vaccinations in elderly, once a month for 3 consecutive months, significantly prevent the AURTI and can increase the IFN-γ level as Th1 response and IL-10 as Treg response in the period of the study.
BCG has also been used for decades to boost immune system in fight against gallbladder cancer, as immunotherapy:
So given that
a) we know the safety profile of BCG, and people can evaluate if they're at risk of any adverse reactions (largely minimal) from getting it, and
b) it does seem to boost immune system, broadly and against the upper tract respiratory infections in the elderly (in addition to many other studied benefits for youth)
It seems that the negative costs of getting it (refreshed) are nearly 0, whereas the benefits are >0 and potentially great. On this basis, the recommendation makes sense, IMO (for anyone who isn't at a risk of some complication from BCG, based on the safety profile).
There's a theory that BCG vaccine (TB) helps strengthen you against corona, I'd recommend getting it if you haven't, or especially for your older relatives (given that the cost/side effects is well-understood and near-zero, whereas the benefits based on the below could be serious):
https://foreignpolicy.com/2020/03/24/coronavirus-vaccine-health-care-workers-bcg/https://www.france24.com/en/20200326-australians-trial-tb-vaccine-to-fight-coronavirushttps://www.medrxiv.org/content/10.1101/2020.03.24.20042937v1 (looking at the correlation between vaccination rates by country and corona spread).
Very speculative: there are different strains of BCG, and allegedly the old (Soviet/Japan/Brazil) type/types is better. This could theoretically explain the different corona case loads between West/East Germany and between Japan + Thailand + Taiwan vs China + Iran (different vaccine strains).
Here are images showing differing corona case loads between East/West Germany (East uses/used the Soviet vaccine), supposedly the population density does not explain this (though note travel patterns, testing rates, etc. are probably all different):
Much more at https://www.jsatonotes.com/2020/03/if-i-were-north-americaneuropeanaustral.html?fbclid=IwAR2MKAgIt2IRjPSf_S9F4HozW4z7BWjH9_9D5p3RmGGJtdh2wp5gkpdzOj8&m=1. If someone who actually understands vaccines could read this and provide thoughts and vet, that'd be great. If it does end up making sense, please do spread, given the high expected value benefit here. I just don't know how easy it'd be to find old (Soviet etc.) style vaccines in the West.