The FDA says "Antibody tests look for antibodies in your immune system produced in response to SARS-CoV-2, the virus that causes COVID-19. " Antibodies can take several days or weeks to develop after you have an infection. Samples for antibody tests are typically blood from a finger stick, or blood drawn by your doctor or at CVS, Walgreens and other medical testing professional..
COVID-19 Antibody Test are typically used to:
The Israeli study of 700,000 people said COVID recovery gave Israelis longer-lasting Delta defense than vaccines. Natural immunity was 27 times better, meaning, the variant was 27 times more likely to break through Pfizer protection from January-February and cause symptoms than it was to penetrate natural immunity from the same period Note that the study also found that one dose of a COVID-19 vaccine improved protection for infection survivors, so the decision to get a vaccine or boosters (or not) remains a case-by-case decision based on the individual's specific circumstances and evaluation of risk. The entire Israeli study is published here.
A Washington University study found that even a mild COVID-19 infection resulted in long-lasting immunity.
The FDA and CDC are trying to discourage antibody testing to determine if individuals have antibodies from a past infection and therefore a level of immunity to COVID-19 and it's variants. The CDC specifically says antibody testing is not currently recommended to determine if you are immune to COVID-19 following COVID-19 vaccination.
Reuters says they often miss past COVID infections, in other words there are false negatives.
Antibody tests one week after first symptoms only detected 30% of people who had COVID-19. Accuracy increased in week 2 with 70% detected, and was highest in week 3 (more than 90% detected). Little evidence was available after week 3. Tests gave false positive results in 2% of those without COVID-19.
A negative result means the test did not detect antibodies to the virus that causes COVID-19. A positive result means the test DID detect antibodies to the virus that causes COVID-19, and it is possible that you had a recent or prior COVID-19 infection and you have developed a natural adaptive immune response to the virus.
The T-cell tests sequences the long-lived SARS-CoV-2–specific memory T cells and complements antibody testing to provide a better picture of previous exposure to SARS-CoV-2. One company offering the tests, T-Detect, claims that T-cell testing outperforms antibody testing. Duke-NUS Medical School has also developed a test, Cytokine Release Assay (CRA), which they say can reliably identify and quantify specific T cells present in the blood of people who have been vaccinated against COVID-19, or have recovered from SARS-CoV-2 infection, but it is not yet on the market.
Most of the reliable information is coming from research and clinical studies conducted in other countries, notably, Israel, Denmark, the UK and Scandinavian countries. The FDA, CDC and US medical authorities have remained oddly silent about COVID-19 antibodies. Clearly, they wish to push vaccination. We'll leave it to others to debate why that is, but it is certainly true. Joe Biden recently said that he believes the U.S. needs to have 97%-98% of its population vaccinated against COVID-19. The following from Whitehouse.gov:
Q How many - how many Americans need to be vaccinated for us to go back to normal? Like what is the percentage of total vaccinations that have to be deployed?
THE PRESIDENT: Well, I think - look, I think we get the vast majority - like is going on in so many - some industries and some schools - 96, 97, 98 percent. I think we’re getting awful close. But I’m not the scientist.
Amazingly, this completely ignores the effect of antibodies from a previous COVID-19 infection. A study of 700,000 people in Israel found that natural immunity provide stronger and longer lasting immunity to future infections than the vaccines did. There is an interesting opinion piece in the Wall Street Journal regarding the lack of research in the US regarding this: see Covid Confusion at the CDC, Decisions on boosters relied on data from Israel. Why isn’t the U.S. producing this research? By Marty Makary Sept. 13, 2021
COVID-19 tests are designed to check broadly for the SARS-CoV-2 virus, including the SARS-CoV-2 delta variant, so yes, antibody and T-Cell tests should pick up past infection from any variant.
Quest Diagnostics - Quest Direct - Around $75. This COVID-19 Antibody Test is a spike protein test which can detect antibodies from a prior or recent infection, regardless of whether symptoms were present. Positive results may also occur after a COVID-19 vaccination, but the clinical significance is not yet known, nor is it known how good this test is at detecting antibodies in those who have been vaccinated. Alternatively, a nucleocapsid test can only detect antibodies from a prior or recent infection. This semi-quantitative COVID-19 Antibody Test provides a positive or negative result and a numerical value that can show your immune response over time if you use the same test.
Aside from through your physician, there is a company, T-Detect, offering an online/home option.
This test has not been FDA cleared or approved but has been authorized for emergency use by FDA under an EUA. Testing of venous whole blood using K2 EDTA specimens is limited to laboratories designated by Adaptive Biotechnologies Corporation that are certified under the Clinical Laboratory Improvement Amendments of 1988 (CLIA), 42 U.S.C. §263a, and meets the requirements to perform high complexity tests as described in the T-Detect COVID Standard Operating Procedure that was reviewed by the FDA under this EUA. This test has been authorized only for detecting and identifying the presence of an adaptive T-cell immune response to SARS-CoV-2, not for any other viruses or pathogens. The emergency use of this test is only authorized for the duration of the declaration that circumstances exist justifying the authorization of emergency use of in vitro diagnostics for detection and/or diagnosis of COVID-19 under Section 564(b)(1) of the Federal Food, Drug and Cosmetic Act, 21 U.S.C. § 360bbb3(b)(1), unless the declaration is terminated or authorization is revoked sooner. T-Detect™ COVID is not indicated for use in patients under age 18.
If you want to be sure the test you are buying is authorized by the FDA, see the FDA tables of molecular, antigen, and serology and adaptive immune response in vitro diagnostic emergency use authorizations (EUA).