A: Unfortunately, no.
TL;DR:
đź’ĄOur current antibody tests can’t tell us how well someone is protected from COVID-19 infection or disease.
Whether you have been previously infected, vaccinated, or a combination of the two, the recent authorization of booster shots in many countries has people wondering if they need one yet.
While it would be great if we had a reliable biomarker 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.
Some antibody tests detect antibodies induced by infection (those targeting the nucleocapsid protein), while others detect antibodies against the now famous spike protein induced by both infection and vaccination.
So, if you got the nucleocapsid antibody test but were only vaccinated, it would come back negative, but this doesn’t mean you are not protected.
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 there are other parts of the immune system such as memory B and T cells that are not detected by antibody tests so even this threshold doesn’t tell the whole story.
Even when antibodies are detected, we don’t know what levels are protective. There is a correlation between binding and neutralizing antibodies, but it’s not perfect.
We certainly believe 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.
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.
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 and quest for accurate correlates of protection 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 booster shots.
âť“How should you decide? Booster recommendations are currently being made based on the totality of the evidence across populations (meaning averages). We know 3rd doses boost antibody levels substantially AND we are seeing this translate into further drops in infection and disease (in Israel and new Pfizer booster trial data for instance).
We recommend getting a booster when available to you based on the eligibility (by age, underlying conditions, occupational exposures, etc). These criteria will likely be expanded over time if evidence continues to mount of the benefit of 3rd doses.
Love,
Those Nerdy Girls
Links:
The Flawed Science of Antibody Testing for SARS-CoV-2 Immunity
What is the difference between antibodies from vaccination and antibodies from having had COVID-19?
