Doctors and experts that SVT has talked to all highlight two factors that they believe have affected: lessons learned and medicines.

- Over time, we have learned more about when and how to use respiratory therapy. That we should give higher doses of blood thinners because there is a risk of blood clotting. And the use of cortisone seems to have positive effects, says Björn Persson, head of operations for intensive care at Karolinska.

In the video, reporter Johan Wikén lists three theories about why mortality has decreased.