That was the original intent of the Covid-19 tests that looked at blood anti-bodies. They could answer the question "Have I previously been exposed to the SARS-CoV-2 virus?" in a YES or NO manner.
More recently, people have mistakenly believed that these tests could accurately answer the question "How strong is my immune response to either the virus or one of the vaccines?" And "does my immunity hold up over time, or does it drop?" These test were never designed to do that. They are a simple YES/NO test, not a quantitative measure of how much immunity is there. With these simple antibody tests, there is a big difference between the two.
The antibody test is like an engine heating warning light on your car's dashboard. It lights up only if the engine is too hot. It doesn't show you what temperature it is.
I believe this is the main thing the JAMA editorial (linked to by TLSGuy in a post about a week ago) was getting at. The editorial cites a NYT article that apparently describes very dubious claims being made by some entities that peddling antibody tests (I have not read the NYT article yet, but it seems to me that someone reading their promotional material could easily be misled).
Here are couple snips from the JAMA editorial:
>>>
The Flawed Science of Antibody Testing for SARS-CoV-2 Immunity . . . [A]s the pandemic unfolded, the concept of an immunity passport based on having antibodies didn’t pan out. The early consumer tests’ accuracy was unproven, making the results somewhat dubious. More fundamentally, the so-called correlates of protection were unknown. Which specific antibodies guarded against SARS-CoV-2 reinfection? How high did their levels need to be? And how long would they provide a reliable defense? . . .
The SARS-CoV-2 serology tests that eventually received FDA Emergency Use Authorization (EUA) have demonstrated
high sensitivity and specificity, but that accuracy is for detecting antibodies.
Their ability to predict protection against the virus based on those antibodies hasn’t been proven. Plus, the FDA cautioned that some tests detect antibodies the immune system likely produces only after natural infection with the virus. Depending on the assay, people who weren’t previously infected could test negative for antibodies despite having vaccine-induced immunity.
Therefore, the agency in its May 19 communication stated that “results from currently authorized SARS-CoV-2 antibody tests should not be used to evaluate a person’s level of immunity or protection from COVID-19 at any time, and especially after the person received a COVID-19 vaccination.”
The problem isn’t simply that the tests weren’t designed to assess immunity, experts told
JAMA. It’s also that the protective antibodies and their thresholds still haven’t been fully worked out.
In an email, Nicole Doria-Rose, PhD, a staff scientist and chief of the Humoral Immunology Core at the National Institutes of Health’s Vaccine Research Center, noted that antibodies that bind to the SARS-CoV-2 spike protein—particularly neutralizing antibodies—“do correlate with protection.” For example, higher titers were associated with increased protection in 2 phase 3 studies: one not yet peer-reviewed of the mRNA-1273 (
Moderna) vaccine and another of the ChAdOx1 nCoV-19 (
Oxford/AstraZeneca) vaccine. Still, she wrote,
“it’s not a simple relationship—there is no clear titer at which you can say whether a particular person is protected.” What’s more, different neutralizing antibody thresholds, or even different immune responses altogether, may correlate with protection against asymptomatic, symptomatic, or severe disease.<<<
This Medical News article discusses why experts recommend against patients getting antibody testing to assess their protection from SARS-CoV-2 after vaccination or infection.
jamanetwork.com
