WHAT IS THE PURPOSE OF THE CORONA ANTIBODIES ASSAYS?
Authors: Daniel Maller, DVM
Contributors: Irene Fermont, MD, MSc,
Immuno-hematology & Pharmacovigilance
Published date: 14 February 2021
1- ANTIBODIES - DEFINITION AND ORIGIN
An antibody is a protein produced by the body's immune system when it detects harmful substances, called antigens. Examples of antigens include microorganisms (bacteria, fungi, parasites, and viruses) toxins, and chemicals. Each type of antibody is unique and defends the body against one specific type of antigen.
Antibodies are synthesized by a particular type of white blood cells: the lymphocytes B type.
2- ANTIBODIES IN NATURAL IMMUNE RESPONSE
● The first line of defense: innate (non-specific) immunity :
In case of infection, the immune system activates immune cells that "patrol" the bloodstream and will
○ partially destroy infectious agents in a non-specific way
○ "introduce" the infectious agent to B and T lymphocytes.
Specific adaptive immunity is then immediately triggered.
● The second line of defense: adaptive (specific) immunity:
This is a specific response against the pathogen.
○ B and T lymphocytes first learn to identify the pathogen that has now been "introduced" to them;
○ The B cells then produce antibodies specific to this pathogen (in about a week).
○ T-cells start destroying infected cells.
These B and T lymphocytes disappear after infection, but a group of "memory" B and T lymphocytes remain in the body.
In the event of a new infection, they will identify the pathogen, they will be immediately reactivated and lead to a specific, effective, and much faster (few hours to less than 48 hours) response.
3- DOES THE ANTIBODY ASSAY REALLY PROVIDE INFORMATION ON THE DEGREE OF PROTECTION?
After the infection of SARS-CoV2
In COVID 19 disease, a normal immune response takes place (except probably in severe forms that would correspond to a runaway of certain mechanisms). One week after contamination, circulating antibodies will appear in the blood of this person. Their dosage shows a peak around the third week, then their number gradually decreases. An American study shows that they remain in the blood for 6 to 8 months. This suggests that the organism is protected during this time by humoral immunity.
After the vaccines
The mechanism of vaccines is to induce the same immune response without the disease in introducing only the pathogen antigens or toxin or the mRNA to produce this antigen, such as the Pfizer-BioNTech and Moderna vaccines.
Several studies realized in Israel in Ichilov and Hadassah Medical Centers have shown that almost all the vaccinated people with 2 shots have a high level of antibodies with the Pfizer vaccine. 
The medical relevance of the antibody assays
The interpretation of the assay results is nevertheless very difficult when the level of circulating antibodies is low after an infection: antibodies are, in fact, only one element of the immune response, and the body's immunity also relies, to a large extent, on cellular immunity and memory immunity both of which are much more difficult to quantify and not routinely performed.
Therefore, it is also not useful to realize the antibody assay either before being vaccinated or after the vaccination, and this for two reasons: the 95% efficacy of the m RNA vaccines has been shown on clinical criteria, i.e. to protect for symptomatic severe or moderate forms of infection, and because when performed, the assays show the presence of antibodies in almost all of the vaccinated.
In conclusion, the assay of circulating antibodies, which can confirm infection with SARS-COV2 or vaccination, gives a partial indication regarding the intensity or exact nature of protection, which is a matter of adaptive humoral immunity as well as adaptive cellular immunity and memory humoral and cellular immunity.
American study :
Data from Hadassah Medical Center, not published