In February or March of 2020 there were two interesting and not well distributed studies. That of immunity of heavy smokers - and/or those who were heavy smokers but had quit, and the other was about the effects of hibiscus on the mucosal lining of the lungs preventing respiratory infection.

I'm overburdened right now, I can't deal with any more COVID studies. But when I read the title and seeing some comments I wonder if the prior art is related.