A Wall Street Journal piece citing a "large national study".

  • Hospitalized Covid-19 patients who received transfusions of blood plasma rich with antibodies from recovered patients reduced their mortality rate by about 50%

The study was presented last weekend so I am not sure why the Journal is saying this is an 'exclusive'. But, there you go.

More:

  • researchers said they saw signs that the treatment might be working in patients who received high levels of antibodies in plasma early in the course of their illness
  • based their conclusions on an analysis of about 3,000 patients

Here is link to the piece (may be gated)