By doing an analysis for the level of antibodies, experts determine how protected the body is from coronavirus. But it is difficult for an ordinary person to understand the abundance of numbers.
Edition “360” tried with the help of reputable experts to figure out what exactly is measured, what tests are done for this, and what BAU is. Corresponding member of the Russian Academy of Sciences virologist Sergei Netesov helped him in this.
To assess immunity to a specific infection, it is necessary to measure the level of specific antibodies of the IgG class to the S-protein of the coronavirus. Different test systems use different measurement methods. However, only a few of them give the final result in the value of Binding Antibody Units (BAU) – units of antibody binding per milliliter. The specialist explains:
“A number of scientific publications have estimated that if the level is above 500, then a person is 99% not seriously ill when infected with the delta variant, and there will be no death.”
At the same time, test systems from different developers determine the BAU value in different sensitivity limits. For example, for Abbott Architect, its upper threshold is 6000–7000, and Vector-Best measures up to 500 BAU / ml – if the value is higher, then the test shows that it is higher than 500. That is, Netesov explains, “above 500 is good below 200 – you need to be vaccinated.
However, there is no single consensus in assessing the level of antibodies for protection yet. After all, only humoral * immunity can be measured this way, but there is also cellular immunity. Therefore, for those who are not related to medicine, experts advise not to rack their brains over deciphering complex tests, but simply to revaccinate every six months, Netesov notes.
For an example of decoding, you can consider the results of a test conducted by the Central Research Institute of Epidemiology of Rospotrebnadzor (the Abbott Architect test system was used). His result of 1824.8 is the BAU value per milliliter. In our example, the value is above 500, that is, the body is protected, the level of IgG antibodies is sufficient.
In the study of antibodies, the method of enzyme immunoassay is used. The virologist explained in detail and in order how the procedure goes:
“There is a pure protein S, that is, the surface protein of the spike of the coronavirus. It is adsorbed onto special tablets or balls. They take a serum sample from a person, it is poured into a cell where this ball is placed. Incubate for some time. A special compound is added in the form of goat, ram antibodies chemically combined with a special enzyme. With the help of such a conjugate, the level of antibodies attached to the S-protein is determined. It is added to a cell or to a ball where antibodies from the test serum were adsorbed, kept and washed. And then they check by the activity of the enzyme in the conjugate, how much of it is bound to the adsorbed antibodies. This is called enzyme immunoassay.
After that, a measurement is taken and the result is converted to BAU per milliliter. Despite the fact that more than a hundred such test systems have been registered in Russia, only a few can be trusted, the virologist warns.
Background: Humoral immunity is a form of immunity that is directed mainly to extracellular antigens and is necessary to protect the body from bacterial pathogens and toxins.