COVID-19 Antibody levels: More may be better

Since the beginning of the COVID-19 pandemic, there’s been a lot of talk about testing. Usually, people are referring to diagnostic testing performed with a nasal swab. However, another type of testing—one that requires a blood test and that you may not know about—has been around nearly the whole time.

That testing is for assessing antibody levels against SARS-CoV-2, the virus that causes COVID-19.

What are antibodies and what do they do?

Antibodies are large ‘Y’ shaped molecules produced by the B-Cells of your immune system. The job of an antibody is to grab on to a foreign invader in your body, or “antigen.” This flags the invader for elimination by other parts of the immune system.

Antibodies have two main parts: the arms and stem of the ‘Y’. The tops of the arms are where antibodies bind, or grab on to things. If you stood up and raised your arms in the shape of a ‘Y’, your hands would be exactly where an antibody grabs onto foreign molecules. Your legs would be the stem.

Once your body forms antibodies to a foreign invader, it keeps a memory of that specific antibody and can produce it again if necessary. This is how some vaccines work: they prepare your body to fight off a real threat by tricking your system into producing antibodies to a simulated threat.

What information does antibody testing provide?

When your physician orders antibody testing, often referred to as serology testing, they are looking for the presence of antibodies (qualitative testing) or the level of antibodies (quantitative testing) you have against a specific target, such as a virus. These tests can tell your physician that you have had an immune response to a virus or vaccine. If the test is quantitative, it also tells your physician the antibody levels against the virus that are currently in circulation within your blood. Usually, these antibody levels provide your physician insight as to the effectiveness of your immune response and sometimes ongoing immunity.

For the pandemic, we’ve mostly ended up with “semi-quantitative” antibody testing. These tests measure the number of antibodies in a patient sample. These assays, or evaluations, have not been correlated to one another so values generated by one assay cannot be compared to values generated by another. Also, the antibody levels that correlate with protection from infection, re-infection or severe disease have not yet been determined for any of the assays.

Is there any new data about SARS-CoV-2 antibody levels?

Recently, specialists have published new scientific evidence in top peer-reviewed science journals. These new data show that, when patient samples were analyzed with the semi-quantitative assay that Labcorp is running, higher levels of antibodies correlated with higher levels of neutralizing antibodies, which, in turn, have been correlated with increased protection from infection, reinfection and severe disease .^1,2

Additionally, specialists found that when it comes to the neutralization of SARS-CoV-2, at least in this context, more seems better. In response, Labcorp has updated the reportable range of its semi-quantitative assay from 2500 Units/mL to 25,000 Units/mL to support reporting of levels higher levels of antibodies.

Who should get an COVID-19 antibody test?

Much is still unknown about antibody levels and how they correlate to immunity, so there’s limited clinical usefulness to these tests. As the newly published data makes a correlation with higher antibody levels and protection from infection and reinfection, it’s understandable that you may want to know what your antibody level is.

If you’ve been infected with COVID-19, been vaccinated or been boosted (or any combination thereof), you might be interested in knowing your antibody level. Unfortunately, these tests cannot tell you how high or low your level is relative to others, or what your particular level may mean for protection.

References:

1. Gilbert PB, Montefiori DC, McDermott AB, et al. Immune correlates analysis of the mRNA-1273 COVID-19 vaccine efficacy clinical trial. Science. 2022;375(6576):43-50.
2. Garcia-Beltran WF, St Denis KJ, Hoelzemer A, et al. mRNA-based COVID-19 vaccine boosters induce neutralizing immunity against SARS-CoV-2 Omicron variant. Cell. 2022;185(3):457-466.e4. doi:10.1016/j.cell.2021.12.033