The US Food and Drug Administration issued an emergency-use authorization on August 23 to treat COVID-19 with convalescent plasma. This makes it easier for hospitals to offer the treatment to some patients.
The problem with the convalescent plasma studies so far is the lack of clinical trials including control groups that don’t receive the treatment. The other large problem is that not all plasma is the same:
convalescent plasma from different people varies widely in antibody concentration, making it challenging to study. At first, researchers had no way to measure and standardize the level of antibodies in each batch. Even now, researchers in some parts of the world are not able to test whether plasma contains powerful ‘neutralizing antibodies’, which can prevent viral replication, because the assay is expensive and requires certain containment procedures