Don’t Use Antibody Tests Post Vaccine to Determine Immunity
Robert Gorter, MD, PhD.et al.
June 3rd, 2021
The U.S. Food and Drug Administration (FDA) issued a safety communication in May 2021, warning both the public and health care providers not to use SARS-CoV-2 antibody tests to gauge immunity, especially after the COVID-19 vaccination.
There’s a significant difference in the immune response triggered by natural infection and vaccination
In the case of COVID-19 mRNA vaccines, such as those produced by Pfizer and Moderna, antibodies to the spike protein are induced; in the case of natural SARS-CoV-2 infection, nucleocapsid proteins are detected by antibody testing
Because of this, people who have received a COVID-19 vaccine and haven’t previously been infected will receive a negative antibody test, provided the test doesn’t detect the vaccine-induced spike protein antibodies
A positive result from a SARS-CoV-2 antibody test could indicate the previous infection or could also be caused by the vaccine
Antibodies are proteins your body makes in response to infections and will be detectable in your blood after infection as a sign of your body’s battle against that pathogen. Antibodies for COVID-19 are believed to develop within one to three weeks after infection, and a positive antibody test for COVID-19 means that a person may have been infected with SARS-CoV-2, the virus that causes COVID-19, in the past.
Titer blood tests, which measure the presence and amounts of certain antibodies in your blood, are sometimes used to prove immunity to a disease. If your titer is positive, which means it’s above a set value, you’re considered to be immune to the disease, such as measles, mumps, or rubella.
This is why, for instance, proof of prior diagnosis with chickenpox, measles, and mumps is allowed instead of vaccination to enter most U.S. public schools — once you’ve had the disease and recovered, you are immune life-long.
In the case of COVID-19, however, the U.S. Food and Drug Administration issued a safety communication in May 2021, (5) warning both the public and health care providers not to use SARS-CoV-2 antibody tests to gauge immunity,