Q: Will it help me know if I’m already immune and can safely go about daily life?
A: No….not yet. While the many antibody test being marketed are improving rapidly, there are still too many fundamental challenges in order to use these as a tool for knowledge about your *individual* exposure or immunity.
Very briefly, antibody tests are (typically) blood tests that aim to measure previous exposure to SARS-CoV-2 by testing for the presence of antibodies specific to the virus, which start to build up one to two weeks after initial infection. These are distinct from the PCR tests conducted via nasal swabs that detect *current* infection by detecting the presence of the SARS-CoV-2 genetic material.
So what are the current limitations of antibody tests for personal use?
1.) UNKNOWN IMMUNITY: Even for those who definitely have had COVID-19, we don’t know the extent or duration of immunity conferred. Since the virus is new, it will take time to follow people who have recovered and see how much protection they have from a new SARS-CoV-2 exposure and how long this protection lasts. The good news is based on the evidence from the lab on the presence of neutralizing antibodies in recovered patients and data from previous SARS and MERS patients, the best current guess is some protective immunity will be conferred for hopefully at least 1-2 years. Still, even knowing for sure you have been exposed isn’t a scientific green light for lack of precautions.
2.) FALSE POSITIVES: Because of the limitations of current tests *and* the low overall prevalence of COVID-19 in the population, many positive antibody tests will be “false positives.” To see a worked example of why this is the case, I refer you to this nice explainer from COVIDexplained. This creates a dilemma if you receive a positive test, as you could be either a “true” positive OR a “false” positive, and thus have not gained any certainty about your previous exposure. This is less of a problem when we estimate population-level seroprevalence, as we can put bounds around this type of uncertainty and for example estimate that 3-5% of the population has been exposed in one location versus 20-22% in a different location. This gives us valuable information at the population level but is less useful for accurate individual prediction.
3.) WHAT WOULD YOU DO WITH THIS INFO? For both of the reasons listed above, changing your behavior with regards to COVID-19 prevention or protecting vulnerable family members after a positive antibody test at this stage would be unwise. Since you can’t readily act on the test results, we recommend saving your money for the time being. As the technology improves the Nerdy Girls will have your back with updated recommendations!
This Atlantic article from last month is still give a great overview of current issues around antibody testing.
