After I’ve Received my Vaccine, should I get a Blood Test to see if I have Antibodies for Covid-19?
Throughout the pandemic, the utility of antibody tests for different purposes has come into question a few times. Early on in the pandemic, many people wished to have their COVID antibodies checked in the hopes that they had in fact already been exposed and had just had very mild disease. Later on, people who had already had symptomatic COVID were interested in checking their serologies to determine if they still had immunity. Now people look to antibody tests wondering if they even need to be vaccinated given previous disease or exposure (the answer is yes) or some are hoping to prove that their vaccine worked. Unfortunately, the antibody tests currently available have not always been able to provide us with clear answers as we don’t yet completely understand all the specifics of COVID immunity after actual asymptomatic or symptomatic disease or after COVID vaccination.
As of now, the CDC continues to advise against antibody testing for the purpose of assessing for immunity after vaccination. Clinical trials revealed that both the Pfizer and the Moderna vaccines effectively protect against developing moderate to severe symptoms from the virus (at rates of 95% and 94% respectively). It is important to clarify that the efficacy of the vaccine is not simply measured by positive antibody tests. On the contrary, many vaccinated individuals are actually likely to test negative.
This is because many of the commercially available antibody tests only detect viral particles from those who had COVID-19 (nucleocapsid proteins) and do not detect the specific antibodies that an immunized person develops (antibodies to the spike protein of the virus). Additionally, even if the antibody test is specific for post-vaccine antibodies, it is possible that an individual’s antibody level would be lower than detectable, but could still provide the person with immunity. There are a few different components of our immune systems that respond to the vaccine and it is likely that a successful immune response against COVID relies on more than just the neutralizing antibodies.
So, unless you are involved in a study or have a special circumstance that requires an antibody test, you do not need to have your antibodies checked after vaccination. If you are worried that you may have been exposed to COVID or have any symptoms, you should have a COVID test done as soon as you can. Prior receipt of a COVID-19 vaccine will not affect the results of SARS-CoV-2 PCR or antigen tests.
Jackie Phillips, MD, April 20, 2021