A: Unfortunately, no.
💥Our current antibody tests can’t tell us precisely how well someone is protected from COVID-19 infection or disease.
Whether you have been previously infected, vaccinated, boosted or a combination of the three, the recent authorization of additional booster shots has people wondering if there is a way to tell if you need it.
While it would be great if we had a reliable “correlate of protection” to measure current immunity levels, sadly we don’t.
Existing commercially available antibody tests are designed to detect *the presence* of binding (not neutralizing) antibodies.
If NO antibodies are detected from a spike protein antibody test after vaccination, this could indicate low levels of protection. This can be the case after vaccination in people who are immunocompromised and is one reason boosters were recommended first for this group. But even then, there are other parts of the immune system such as memory B and T cells that are not detected by antibody tests so the test doesn’t tell the whole story about protection.
Even when antibodies are detected, we don’t know exactly what levels are protective. There is a correlation between binding and neutralizing antibodies, but it’s not perfect.
We know that higher neutralizing antibodies are better on average (as seen by their ability to neutralize live virus in a lab dish), but we really don’t know *how high is high enough* for any given individual.
*For a March Madness basketball analogy, think about the relationship between height and success in college basketball. We all know that height and basketball success are strongly correlated. BUT there is lots of variation around this- some short people are successful in the NCAA, and plenty of tall people are NOT good basketball players. So you can’t predict someone’s basketball talent based on their height alone.
This type of variability helps explain why even though we know that MORE antibodies give better protection against infection on average (and being tall is associated with better basketball prospects), we can’t predict protection for an individual person based on their antibodies.
Levels of antibodies were correlated with chances of getting infected in the Moderna COVE clinical trial (see link below)—meaning higher antibodies ➡️ lower chances of being infected. This is the best kind of data because it links antibodies to *actual* infections. But even these data couldn’t give a specific protective threshold. People who got infected on average after vaccination had lower antibodies than those who didn’t. But there was plenty of overlap in the antibody levels of infected and non-infected.
The COVE trial also took place in a different pandemic context— pre-boosters and pre-variants, so it’s unlikely any specific thresholds would apply to our boosted + Omicron new world anyway. With immune-evading variants, correlates of protection will be a moving target.
Another wrinkle is that laboratory tests are not standardized in their scales, meaning comparisons of levels across tests is difficult. We assume that this standardization will improve over time, but we are not there yet.
⬇️ BOTTOM LINE:
There is currently no test that can tell you your individual level of protection from COVID-19 infection. These tests are thus not a good way to decide about whether you should get a booster shot.
People with high antibody levels are still seen in the hospital, while people with low antibodies can still fend off infection. We don’t yet have that elusive “correlate of protection” that clearly tells us the probability of infection or disease based one or more biological markers.
❓How should you decide? Booster recommendations are currently being made based on the totality of the evidence across populations (meaning averages). We know 4th doses boost antibody levels and likely protection, which is especially important for older and more vulnerable people.
Those Nerdy Girls
“Antibody testing is not currently recommended to assess for immunity to SARS-CoV-2 following COVID-19 vaccination, to assess the need for vaccination in an unvaccinated person, or to determine the need to quarantine after a close contact with someone who has COVID-19.”