At this moment of the pandemic, a very critical point is to know if each of us is immunised and at the same time if is contagious or no. To know if people are immunised against COVID-19 is essential information to be able to undo this state of quarantine in which we are immersed. Only people who have been infected, but are already non-contagious, could return to their normal lives, allowing a progressive return to our previous routine. For this reason, it is essential to analyse the antibody load that each person presents. Therefore, the combined of an RT-PCR + a rapid serological test (for antibodies detection) is what should be imposed as a requirement to return to normality. First, a serological test could tell us if we have antibodies against the virus and only in the case we have specific antibodies in our blood, a confirmation by RT-PCR will be required to ensure that we are not infectious. A positive IgG with an already negative IgM, practically wouldn´t require confirmation by RT-PCR, but sometimes the virus or its proteins are maintained in blood for longer time. Thus, there exist different possibilities:
|Test results||Significance||Return to normal Life?|
|+||-||-||You are in the first days of infection (antibodies, IgM, are the first antibodies in appearing, they normally require 4 to 5 days in being detected). You are contagious.||NO|
|+||+||-||You are in the early stage of infection. Although you have IgM antibodies in your blood, you are still contagious.||NO|
|+||+||+||You are in the active phase of infection. You are immunized with IgM and IgG antibodies, but you are still contagious.||NO|
|+||-||+||You are in the late or recurrent stage of infection. You are immunized, you already have only IgG antibodies, but you still are contagious.||NO|
|-||+||-||You are in the early stage of infection. It is highly probable that the RT-PCR would be a false-negative. Very suspicious…you should repeat the RT-PCR test.||Before, let ensure your RT-PCR result|
|-||-||+||You have had a past infection and has recovered. You are immunized and not contagious anymore.||YES!!!|
|-||+||+||You are in the recovery stage of an infection, but it is possible that the RT-PCR result may be false-negative. You should repeat the RT-PCR test.||Before, let ensure your RT-PCR result|
And what is it necessary for accurate antibody detection in patient’s sera? The quality of the IVD test is essential. For this purpose, the test should carry specific antigens in the device (antigen = antibody generators). Antigens are viral proteins which bind their specific antibody in patients´ sera, allowing the development of the rapid test. When it is very dangerous to work with the native virus, the tests use proteins of recombinant nature which should maintain the capacity to bind specific antibodies triggered initially by the native virus. There are several characteristics which make an antigen to be a good candidate for an IVD test:
Therefore, although all rapid tests would seem to be the same, the sensitivity (2) and specificity (3) are critical characteristics that should be considered when you choose an IVD test, being the antigen used in these rapid tests, a critical issue to get good quality essays.
At Rekom Biotech, we design and manufacture these antigens to offer our customer the best raw material for manufacturing their rapid test for Ab detection. Right now, we have developed the COVID-19 nucleocapsid phosphoprotein (NP) recombinant antigen, and we are working on improving the development of a COVID-19 chimera, to increase the number of epitopes in the recombinant antigen.