- Young Population
- Non-obese population
- Heat and Humidity across a lot of the country
- Widespread deployment of anti-malarials to combat malaria
- Wide spread deployment of BCG vaccine
- Tumeric heavy diet compared to the rest of the world
The top 3 are non-controversial. Young, skinny people are less susceptible, and the spread of the virus slows with sunlight, heat, and humidity.
Anti-malarials like Chloroquine, etc. are more controversial, but there is significant anecdotal evidence, as well as in vitro studies indicating they may be helpful. Furthermore, countries that widely deploy anti-malarials for malaria have so far shown lower death rates than expected (Brazil in particular should be on fire with COVID-19).
BCG vaccine for TB appears to help with COVID-19, through a heightened general immune response. Big studies going on right now to test this theory. There are six different formulations of the vaccine and it is unclear if the different formulations effect its potential efficacy against COVID-19. This is even more "on the edge" of science than the anti-malarials, but the BCG vaccine has shown long lasting resistance to all kinds of respiratory ailments in populations where it is deployed.
Tumeric is flat out a stretch. Curcumin has come up over and over again in studies of compounds that may help. But, there is absolutely no testing or real evidence at this time. It is merely a supposition based on molecular models and meta-studies of other studies on the compound. I included it for discussion, since Tumeric consumption is likely higher in India than many other countries. I also wonder if it plays any role in traditional medicine in the country.
People look for a silver bullet, but there are many factors at play here.