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


Now that we already have other detection methods to measure the presence or absence of a virus, such as PCR tests or rapid antigen tests, the ideal option is to complete the study followed by a serological test that allows us to check for antibodies against the virus. virus in an infected person

After months of living day after day and even almost hour after hour with news of Covid-19, we are learning more and more about the SARS-CoV-2 virus that causes this disease. As research advances and this knowledge grows, new, more reliable and faster diagnostic tests such as newer antigen tests that can detect possible infections with the same efficiency as classical PCR, with the advantage of getting results in just 15 minutes. Both options continue to coexist with others, such as serological antibody tests, which are also very important 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 a finger puncture) and samples analyzed by ELISA / CLIA methods (obtained by a venous blood puncture), which measure our immunological status compared to virus depending on the IgA, IgM and IgG antibodies produced by our body. Immunoglobulins do not detect the presence of a virusbut our body’s immune response when we are exposed to the virus. That is, they tell us whether a person has been in contact with the virus, whether he has symptoms. As if they were two battle lines against infection, IgM are the first antibodies to appear in the blood. IgGs appear later, 8-14 days after infection, and they can disappear or remain, sometimes even indefinitely. Thus, the results of this test give us information about what phase of infection the patient is in:

  • If only IgM is present in the antibody test, we are probably in the early stages of 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 remnants of the acute phase.
  • When only IgG antibodies are observed, it means that the viral replication phase has passed.

Now that we already have other detection methods to measure the presence or absence of a virus, such as PCR tests or rapid antigen tests, the ideal option is to complete the study followed by a serological test that allows us to check for antibodies against the virus. a virus in an infected person; While we still do not know with certainty what the optimal level of immunity or its duration is, this is the key to finding out if it can cause serious pathology if reinfected. It is true that “we will have to wait months and even years to reliably learn about the consequences of the second coronavirus infection,” according to various groups of scientists, but, in any case, knowledge of the state of immunity is important first of all for all those. people who have had the disease without symptoms, in addition to those who, having had the disease, do not know their immune status.

There is a lot of talk now about vaccination and the strategies that need to be developed for it, but it will not be possible to vaccinate the entire population “at the same time” as the vaccine will be produced and sold gradually.

The importance of herd, group or “herd” immunity is discussed in order to take into account that the development of a pandemic can be controlled and for this it should achieve “optimal” 60% immunity. population approximately. When enough people in a community are protected from a contagious disease, infection becomes difficult to spread. Knowing the immune status of different populations, in addition to identifying the groups at highest risk, can help determine which people should be vaccinated first, as those with sufficient immunity can be vaccinated at later stages if necessary.

Consequently, performing serological immunity tests, which are much more specific, would help us know which subpopulations are not immune, but on the other hand, it would allow us to determine which people have immunity, even if they appear to be did not suffer from this disease.

Since the start of the pandemic Chiron prevention, the professional risk prevention company of the Quirónsalud group, has already performed more than 600,000 COVID-19 tests among both company employees and individuals, and indeed the demand for virus detection tests is growing compared to tests that perform antibody detection, although in fact, according to Dr. Leopoldo Alvarez, “both are complementary tests” and for different purposes, as some allow us to detect the virus and act immediately, curing and / or isolating an infected person, while others help us know the immunological status of a person and the population in overall ”, which can help develop vaccination procedures and strategies based on the availability of different vaccines.

In the workplace, performing serological tests becomes even more important as knowing the percentage of employees in the workforce who have immunity and the percentage of those who do not (negative) should have a direct impact on the measurement protocol. accept and therefore in risk management. Chironprevention recommends the following:

  • If we want to know if employees have symptomatic or asymptomatic cases that may suggest an outbreak situation or risk of infection in the company, we have two options: perform PCR (or antigen test) directly, or perform serological tests and perform PCR only on those people who have IgM antibodies but have not yet developed IgG antibodies.

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

Which test is most appropriate in each case?

Case 1. Until I had any symptoms and I had no close contact * with a positive… An antibody test, a serological test that provides information about a person’s immune status is recommended. If the test result is negative and the specified contact conditions have not changed, it is recommended to repeat the test within a period of time, which 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, it is best to do a PDIA (Acute Infection Test: PCR or Rapid Antigen Test) when you know you are in close contact with a positive result.

If the PDIA result is positive, ChironPrevention recommends that a serological test be performed as soon as possible, and if it shows an IgG + value, this will be considered the end of the case and should not be quarantined or repeated. this moment. The person could return to work. If the Ig G value is -, it is considered an active infection and it will be quarantined for 10 days and a search for contacts will be made.

If the PDIA is negative, there is no need to perform a serological test, isolation or contact lookup and you can continue your work.

Case 3. I have symptoms similar to those of COVID-19. As in the previous case, it is recommended to immediately check for a virus and, depending on the result obtained, proceed as we have already commented earlier.

* This is considered “close contact”, according to the Ministry of Health in its document “STRATEGY FOR EARLY DETECTION, SURVEILLANCE AND CONTROL OF COVID-19”, “with everyone who was in the same location as the case at a shorter distance. 2 meters and more than 15 minutes “.

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