Blood plasma donated by patients that have received any of the COVID mRNA vaccine cannot be used to treat patients who are suffering from a SARS CoV-2 infection. See FDA guidelines that specifically address this issue: https://www.fda.gov/media/136798/download
NOTE: A quote from the FDA guidelines cited above, dated Feb 2021: "Individuals who have never been infected with COVID-19 and have received a COVID-19 vaccine are not eligible to donate . . . plasma. This is to ensure that . . . plasma collected from donors contains sufficient antibodies . . . to COVID-19 infection."