Wednesday, December 2

Serological tests: the importance of knowing the immunity against the virus :: Prensa Ibérica


Now that we already have other detection techniques to measure the presence or not of the virus, such as PCR tests or rapid antigen tests, the ideal is to complete the study with a subsequent serological test that allows us to verify the presence of antibodies against the virus. virus in the infected person

After months of living day after day, and even almost hour after hour, with the news about Covid-19, we are learning more and more about the SARS-CoV-2 virus that causes the disease. As research progresses and that knowledge grows, new increasingly reliable and faster diagnostic tests such as the new antigen tests, capable of identifying possible infections with the same efficiency as the classic PCR with the advantage of being able to obtain the results in just 15 minutes. Both options continue to coexist with others, such as serological antibody tests, which are also highly relevant because they provide very valuable information.

These were the first tests carried out in Spain, both the so-called rapid finger tests (sample obtained by finger puncture) and samples analyzed by ELISA / CLIA methods (obtained by puncture in venous blood), which measure our immunological status against the virus based on IgA, IgM and IgG antibodies developed by our body. Immunoglobulins do not determine the presence of the virus, but the immune response of our body when we have been exposed to the virus. That is, they tell us if the individual has been in contact with the virus, whether or not they have developed symptoms. As if they were two battle lines against infection, IgMs are the first antibodies to appear in the blood. IgGs appear later, from 8-14 days after infection, and they can disappear or remain, sometimes even indefinitely. Therefore, the results of this test provide us with information on what phase of the infection the patient is in:

  • If when an antibody test is carried out, only the presence of IgM is observed, we are probably in the initial stages of the infection.

  • When the analysis shows IgG and IgM, we think that more time has passed since the beginning of the infection and that there are remains of the acute phase.

  • When only IgG antibodies are observed, it is because the viral replication phase has passed.

Now that we already have other detection techniques to measure the presence or absence of the virus, such as PCR tests or rapid antigen tests, the ideal is to complete the study with a subsequent serological test that allows us to verify the presence of antibodies against the virus. virus in the infected person; Although we still do not know with certainty what is the optimal level of immunity or its duration, this is key to find out if, in case of reinfection, it could or not cause a serious pathology. It is true that “We will have to wait months and even years to reliably know the effects of a second coronavirus infection”, according to different groups of scientists but, in any case, knowing the state of immunity is important above all for all those people who have suffered the disease asymptomatically, in addition to those who, having suffered it, we do not know their immune situation.

There is much talk about vaccination and the strategies that will have to be established for it, but it will not be possible to vaccinate the entire population “simultaneously”, since the vaccine will be produced and marketed progressively.

The importance of collective, group or “herd” immunity is discussed, in order to consider that the progression of the pandemic can be controlled and that, for this, it should reach “optimally” 60% of the population approximately. When enough people in a community are protected against a contagious disease, it is difficult for the infection to spread. Knowing the immune status of different population groups, in addition to the establishment of the highest risk groups, can help to establish which people should undergo vaccination as a priority, since those who have sufficient immunity could be vaccinated in later phases, if necessary.

Therefore, performing serological tests for immunity, which are much more specific, would help to know which subpopulations do not have immunity but, on the other hand, it would allow us to identify which people have immunity even though, apparently, they have not had the disease.

Since the beginning of the pandemic, Chironprevention, a company for the prevention of occupational hazards of the Quirónsalud group, has already carried out more than 600,000 COVID-19 tests on both company workers and individuals and, indeed, the increase in demand for virus detection tests compared to those of that perform antibody detection, when in fact, according to Dr. Leopoldo Álvarez, “Both are complementary tests” and with different purposes, since some allow us to detect the virus and act immediately by treating and / or isolating the infected person , and the others help us to know the immunological status of the person and the population as a whole ”, which could help to establish vaccination procedures and strategies based on the availability of the different vaccines.

In the workplace, performing serological tests becomes even more important, since knowing the percentage of employees in a workforce who have immunity and the percentage of those who do not have it (negative) should directly influence the measurement protocol to adopt and, therefore, in risk management. For companies, Chironprevention recommends the following:

  • If we want to know if in a staff there is presence of symptomatic or asymptomatic cases that could suppose a situation of outbreak or a risk of contagion in the company, we have two options: do PCR (or antigenic test) directly, or do serological tests and perform PCR only on those individuals who have IgM antibodies without having yet developed IgG antibodies.

    If what we are looking for is to know what degree of protection the template has, we must do serological tests and determine what percentage of employees have IgG antibodies.

What test is the most appropriate in each case?

Case 1. So far I have not presented any symptoms or had close contact * with a positive. It is recommended to carry out an antibody detection test, that is, a serological test, which provides information about the immune status of the person. If the result of the test is negative and the contact conditions mentioned have not changed, it is recommended to repeat it within a period of time that will depend on the prevalence existing at that time in your environment.

Case 2. I have no symptoms, but I have been in close contact with a positive. In this case, the best thing to do is to carry out a PDIA (Acute infection detection test: PCR or Rapid Antigen Test) at the moment when you are aware of having maintained close contact with a positive.

If the result of the PDIA is positive, the recommendation of Chironprevention is to carry out a serological test as soon as possible and if it presents an IgG + value, it would be considered the end of the case, and no more test should be isolated or repeated in that moment. The person could return to work. If the Ig G value is -, it is considered an active infection and it will be isolated for 10 days and a search for contacts will be made.

If the result of the PDIA is negative, there is no need to perform a serological test or isolation or search for contacts, and you can continue with your work.

Case 3. I present symptoms compatible with those of COVID-19. As in the previous case, it is recommended to test for the virus immediately and depending on the result obtained, proceed as we have commented previously.

* It is considered ‘close contact’, according to the Ministry of Health in its document of COVID-19 EARLY DETECTION, SURVEILLANCE AND CONTROL STRATEGY, “To anyone who has been in the same place as a case, at a distance of less than 2 meters and for more than 15 minutes.”

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