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According to the international definition, the diagnosis of COVID-19 disease is determined only if the PCR test detects the presence of the SARS-CoV-2 virus, or if the RAT (rapid antigen test) test detects the presence of its antigen. The presence of antibodies against the SARS-CoV-2 virus in patient’s blood does not – according to the international definition – prove that they had suffered from the disease.
Antibodies form only a part of the immune protection against the SARS-CoV-2 virus; another part is for example a cellular immunity. Antibodies are proteins that specifically bind to an antigen (e.g., spike protein). They fall apart relatively quickly (in 2 to 23 days in general). The human body is capable of producing more than a million of various antibodies with different compositions, structures, functions, mechanisms, and purposes. Antibodies form only a part of the immune protection against the SARS-CoV-2 virus.
From the information stated above it is clear that the influence of antibodies on the SARS-CoV-2 virus is not easy to decode. A limit, when the protection is sufficient, must be set to be able compare whether a person has enough of antibodies. A complication is also the absence of standardised method for the examination of COVID-19 disease antibodies.
It is not possible to find out when the COVID-19 disease occurred based on the level of antibodies. Therefore, it is not possible to recognise the 180-day period because we are not able to determine the date from which we should count it. The level of antibodies is different and unstable over time for every person – antibodies are disintegrating but growing upon an encounter with an antigen. A Person A can have antibody level right after suffering from COVID-19 disease lower by a half than a person B who have suffered from it two months ago.
There are currently proceeding several studies (e.g., PREVAL II, Czech only) that are exploring antibodies, cellular immunity, and other related topics. With every finished study we get new information that are later used for making the already known information more accurate. Then, based on this knowledge, it would be possible to negotiate about antibodies recognition.