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The article itself did offer the 85% number, for the reduction of hospitalization and death, so there clearly has been some data collection.
Also, these antibody treatments had to have trials to support their Emergency Use Authorizations, just like the vaccines, or any other drug.
The doctors that have posted about it on Free Republic (that I have seen), have been very positive about it - with one important caveat (also raised in the article). There are different types of antibody infusions for COVID, and they not equally safe or effective. That being said, the results are usually profoundly positive, if given early enough (before you need oxygen).
Anecdotally, my good friend who got hit hard with COVID plus pneumonia, reported that the antibody infusion (Regeneron) had him feeling noticeably better in just a few hours, and his fever broke overnight. President Trump and Rudy Giuliani experienced similar results.
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