Obesity is a huge factor. If we had a zero obesity rate I suspect that would cut the infection fatality rate by at least 2/3.

https://www.wfae.org/health/2021-09-30/novant-says-9-of-10-c...

https://cardiologyres.org/index.php/Cardiologyres/article/vi...

https://reason.com/2022/01/03/cdc-covid-19-children-hospital...