In the last days a lot has been written about rapid antibody tests in order to understand if we came in contact with novel coronavirus. But, exactly, how can we interpret these tests? And, may these tests be useful to reduce the lockdown and go back to normal life? An informative appeared a few days ago in the prestigious journal Nature shed some light.
Coronavirus, the virus in the body and the immune response
Coronavirus, like all the other viruses, is formed by a fragment of genetic material, RNA, wrapped by proteins. When the virus enters the body start replicating at the level of the upper respiratory ways and then it may reach the lower respiratory tract. The body replies to the external aggression by producing antibodies that attack the proteins that wrap the viral RNA. But the produced antibodies aren’t all the same. Indeed, a part of antibodies, called IgM, are released in the initial part of infection, are detectable in blood 4-5 days after the contact with the virus and disappear after a few weeks. The antibodies IgG, instead, are produced in a second time, usually after some weeks from infection, and tend to stay for longer.
Coronavirus, how do tampons work
Some biological material is taken from the mucosa of nose and throat to search for the virus presence. If the tampon results positive, this means that the infection is active and that we are potentially able to infect other people.
Coronavirus, how do the antibody tests work?
From a blood sample the antibodies IgM and IgG are searched. If the type IgM is present, then it is likely that we are in a beginning phase of illness. If both the antibodies are detected then it is likely that we are in an intermediate phase of infection, if present only IgG then it is likely that we are in the final part of infection or we are healed. If the test doesn’t detect the antibodies then this means that we haven’t yet come in contact with the virus or that we are in a very beginning phase of infection, the so called window period, but it may also be that the antibodies are present but the test didn’t find them.
Coronavirus, how reliable are the antibody tests and if they may predict immunity
On the basis of these considerations, it is clear that the antibody tests are very useful to understand the people that came in contact with the virus in order to study the diffusion and where the outbreak began. However, it is clear that the test isn’t decisive and to know if the virus is still present and we are able to infect other persons it is necessary to do also the tampons. Indeed, according to a study published a month ago in Nature, the viral RNA decreases slowly after the antibodies have been observed, thus the presence of antibodies doesn’t mean that we cannot be infective (Woelfel et al, Nature, 2020). Finally, as underlined by the same scientists, having the antibodies doesn’t mean that we are immune.