FDA reminds the public and health care providers that results from currently authorized SARS-CoV-2 antibody tests should not be used to evaluate a person’s level of immunity from COVID-19 at any time, and especially after the person received a COVID-19 vaccination.

http://www.fda.gov/medical-devices/safety-communications/antibody-testing-not-currently-recommended-assess-immunity-after-covid-19-vaccination-fda-safety