"Currently authorized SARS-CoV-2 antibody tests have not been evaluated to assess the level of protection provided by an immune response to COVID-19 vaccination. If antibody test results are interpreted incorrectly, there is a potential risk that people may take fewer precautions against SARS-CoV-2 exposure. Taking fewer steps to protect against SARS-CoV-2 can increase their risk of SARS-CoV-2 infection and may result in the increased spread of SARS-CoV-2."
https://www.fda.gov/medical-devices/safety-communications/antibody-testing-not-currently-recommended-assess-immunity-after-covid-19-vaccination-fda-safety
"Antibodies are proteins made by the immune system in response to an infection or vaccination"
https://www.verywellhealth.com/antibodies-from-vaccines-and-from-natural-infection-5092564
"A recent study found that serum levels of antibodies against the spike protein of the virus, which it uses to gain entry to cells, start to wane around 12 weeks after the second dose of the Pfizer vaccine.
The researchers discovered that by 6 months after the second dose, median levels of these antibodies had fallen to around 7% of their peak level, with a range of 2–25%. The researchers say that this decline is expected."
https://www.medicalnewstoday.com/articles/waning-immunity-and-covid-19-vaccines-how-worried-should-we-be
"Higher SARS-CoV-2 antibody levels in fully vaccinated individuals translated to lower rates of infection for nursing home residents and staff during the Delta wave, though not when Omicron hit, a cross-sectional study showed."
https://www.medpagetoday.com/infectiousdisease/covid19vaccine/100702
"Antibody tests can detect the body's levels of antibodies against a certain virus."
https://www.verywellhealth.com/antibodies-from-vaccines-and-from-natural-infection-5092564
BioNTech vaccine creates 10 times higher antibody levels compared to Sinovac: Study in Lancet
https://theprint.in/health/biontech-vaccine-creates-10-times-higher-antibody-levels-compared-to-sinovac-study-in-lancet/697217/
Waning antibody levels after COVID-19 vaccination with mRNA Comirnaty and inactivated CoronaVac vaccines in blood donors, Hong Kong, April 2020 to October 2021
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8759113/
"A vaccinated person is very likely to get a negative result from a serology test, even if the vaccine was successful and protective. That’s because different serology tests detect antibodies to different parts of the virus.
Some tests detect antibodies to the spike protein of the virus, which are produced in response to viral infection or the vaccine. Others detect antibodies to a different part of the virus called the nucleocapsid protein, which are produced in response to infection, but not by the current vaccines.
“A vaccinated person should not be alarmed or worried if they receive a negative antibody test result because this test does not detect antibodies from the Pfizer, Moderna and Johnson & Johnson’s Janssen COVID-19 vaccines, which were developed against the spike protein of the virus,” says Fernando Martinez, M.D., medical director of Laboratory Medicine. “This reinforces the guidance from the CDC that serology tests should not be used to test for immunity.”"
https://www.mdanderson.org/cancerwise/what-do-negative-positive-antibody-test-results-mean-after-a-covid-19-vaccine.h00-159459267.html
"the mRNA will enter the muscle cells. Once inside, they use the cells’ machinery to produce a harmless piece of what is called the spike protein. The spike protein is found on the surface of the virus that causes COVID-19. After the protein piece is made, our cells break down the mRNA and remove it, leaving the body as waste.
Next, our cells display the spike protein piece on their surface. Our immune system recognizes that the protein does not belong there. This triggers our immune system to produce antibodies and activate other immune cells to fight off what it thinks is an infection. This is what your body might do if you got sick with COVID-19."
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/mrna.html
"The mRNA vaccines use a molecule called messenger RNA (or mRNA), rather than the actual pathogen to train the immune system to fight infections.
Viral load -- the amount of SARS-CoV-2 virus found in a test sample -- is not an indicator of how contagious an individual is, though early research suggests it could play a role in disease severity and secondary transmission."
https://www.newindianexpress.com/lifestyle/health/2021/jul/01/covid-19-vaccines-reduce-severity-symptoms-and-viral-load-in-re-infected-people-study-2324051.html