A useful overview of the changes:

Two new peer-reviewed studies are showing a sharp drop in mortality among hospitalized COVID-19 patients. The drop is seen in all groups, including older patients and those with underlying conditions, suggesting that physicians are getting better at helping patients survive their illness….

The study, which was of a single health system, finds that mortality has dropped among hospitalized patients by 18 percentage points since the pandemic began. Patients in the study had a 25.6% chance of dying at the start of the pandemic; they now have a 7.6% chance.

That's a big improvement, but 7.6% is still a high risk compared with other diseases….

 

Horwitz and her colleagues looked at more than 5,000 hospitalizations in the NYU Langone Health system between March and August. They adjusted for factors including age and other diseases, such as diabetes, to rule out the possibility that the numbers had dropped only because younger, healthier people were getting diagnosed. They found that death rates dropped for all groups, even older patients by 18 percentage points on average….

"I would classify this as a silver lining to what has been quite a hard time for many people," says Bilal Mateen, a data science fellow at the Alan Turing Institute in the United Kingdom. He has conducted his own research of 21,000 hospitalized cases in England, which also found a similarly sharp drop in the death rate. The work, which will soon appear in the journal Critical Care Medicine and was released earlier in preprint,shows an unadjusted drop in death rates among hospitalized patients of around 20 percentage points since the worst days of the pandemic.

Mateen says drops are clear across ages, underlying conditions and racial groups. Although the paper does not provide adjusted mortality statistics, his rough estimates are comparable to those Horwitz and her team found in New York….

Doctors have gotten better at quickly recognizing when COVID-19 patients are at risk of experiencing blood clots or debilitating "cytokine storms," where the body's immune system turns on itself, says Amesh Adalja, an infectious disease, critical care and emergency medicine physician who works at the Johns Hopkins Center for Health Security….

But Horwitz and Mateen say that factors outside of doctors' control are also playing a role in driving down mortality. Horwitz believes that mask-wearing may be helping by reducing the initial dose of virus a person receives, thereby lessening the overall severity of illness for many patients.

And Mateen says that his data strongly suggest that keeping hospitals below their maximum capacity also helps to increase survival rates. When cases surge and hospitals fill up, "staff are stretched, mistakes are made, it's no one's fault — it's that the system isn't built to operate near 100%," he says….