Harvard published a study on link between PM2.5 pollution and mortality.
We found that an increase of only 1 μg/m3 in PM2.5 is associated with a 15% increase in the COVID-19 death rate, 95% confidence interval (CI) (5%, 25%)
Places most hit so far are on the more polluted side so one can expect final CFR/IFR be lower than estimated from current data.
There’s a recent paper on the topic “Are Ideas Getting Harder to Find?” According to data analyzed there rate of scientific discoveries in existing fields (e.g crop yields increase, Moore’s law, etc.) remains close to constant while number of researchers constantly increases.