From what test
What do the tests for coronavirus say
Irina Nevinnaya, Rossiyskaya Gazeta
Moscow has announced the start of widespread free testing of residents for antibodies to the coronavirus SARS-CoV-2, which causes the serious disease COVID-19. At the same time, for the third month, everyone who gets a respiratory infection or pneumonia is tested for the presence of the virus itself in the body. Many people are confused: what tests are there, why they are needed and in which cases a person is obliged to undergo an analysis, and in which cases it remains his personal business. Alexander Gorelov, Deputy Director for Scientific Work of the Central Research Institute of Epidemiology of Rospotrebnadzor, Corresponding Member of the Russian Academy of Sciences, answered the questions of Rossiyskaya Gazeta.
– First, about the PCR test, which appeared first in our country: it is an analysis for the presence of a virus in the body, thanks to which the patient is diagnosed with COVID–19 or some other infection. These tests, if the doctor prescribes them, are mandatory. At the same time, the medical community is actively discussing the topic that this testing is not effective enough, there are many false negative results. As a result, the doctors of COVID-departments even agreed to diagnose COVID-19 without waiting for the test results if the CT gives a "picture" of viral pneumonia.
Alexander Gorelov: The test results depend on the quality of diagnostics and on the methods used. In pneumonia, the pathogen is in sputum or in biomaterial taken from the bronchi. If the PCR test is given this way, then the diagnosis will be confirmed. But many patients with pneumonia had a smear taken from the nasopharynx, and this is pointless. There is a phase of the course of the disease, and it must be taken into account. At the initial stage of the disease, a PCR test from the nasopharynx will show a positive result, but if the patient has already developed pneumonia, the virus, relatively speaking, has already "descended" into the lower respiratory tract, and it is necessary to "look for" it there.
As for the fact that the diagnosis of COVID-19 is made even before the test results, we are talking about a preliminary diagnosis in order to start treatment faster. And when the results of the tests become known, the diagnosis is confirmed.
– The second type of tests is for antibodies produced by the body's immune system in response to the ingress of the virus, are they used to diagnose COVID–19?
Alexander Gorelov: Antibody diagnostics can also be used to determine covid pneumonia. But this test may also indicate that a person has already had a coronavirus. Early specific IgM class antibodies appear on the fifth to seventh day of the disease, and starting from the second to third week, the body produces late IgG antibodies. The first ones circulate for up to two months, the second ones for six months and possibly more.
By the presence of IgM antibodies in the blood, one can judge whether a person is sick or not at the moment, and the presence of IgG antibodies indicates that he has already suffered from the disease. This testing also helps to identify those who have had COVID-19 without symptoms.
– Now the version is being actively discussed that those 80 percent of the population who do not get COVID-19, or those who have the disease easily, could have previously had other coronavirus infections, and the antibodies developed protect them from COVID-19. What is your opinion?
Alexander Gorelov: I think this is an absolute misconception. Seasonal coronaviruses circulate constantly, causing SARS and diarrhea in 10-20 percent of the population every year. That is, a person does not have long-term persistent immunity after a coronavirus infection (as, indeed, in the case of influenza). It is no accident that we have to get an annual flu shot. Therefore, there is no reason to believe that, having previously been ill with another coronavirus, we are protected from a new one.
The second point: widespread coronaviruses have not yet led to such severe complications as the new SARS-CoV-2.
Therefore, the population was not tested so widely for these infections before. Therefore, we do not know how long a person remains protected from a new infection after he has been ill. Such studies are just underway, including in Russia.
– Antibody tests, as we are told, are also needed so that a COVID patient can, if desired, become a plasma donor. But opponents of the method warn: if you pour "fresh" plasma with antibodies to COVID, there is a risk of bringing another dangerous infection to the patient.
Alexander Gorelov: Concerns related to the violation of the terms of plasma quarantine are justified. But it is necessary to take into account the specifics of the moment. Plasma transfusion is allowed during the pandemic for vital, that is, vital indications. That is, now we are not talking about mass transfusion of plasma to all patients in a row, but only to those who are between life and death. Such methods are being tested to save them.
But at the same time, everything is being done to minimize the risks: plasma is necessarily checked by highly sensitive express methods for various infections (including HIV, hepatitis) and decontaminated. These procedures are strictly regulated in order to maximize the safety of the method.
If we strictly follow the logic of evidence-based medicine, any medicines and medical technologies should not be used until reliable confirmation of their effectiveness and safety has been obtained as a result of clinical trials. But the epidemic is a special case, hundreds of thousands of people get sick. They should not be left without help, and in such conditions it is allowed to use drugs created earlier for the treatment of other infections, if there is reason to assume that they can help.
– Another argument in favor of testing is the issuance of a certificate that a person has been ill and is not dangerous to others. Some countries are discussing the introduction of "immune passports", although the WHO has stated that there are not sufficient grounds for this yet. Really not?
Alexander Gorelov: As for the initiative to issue "immune passports", in my opinion, this is a rather pointless idea. You may have a large number of IgG antibodies (late antibodies that indicate that a person has suffered a disease), but they will not have the ability to neutralize viruses, and their presence does not guarantee against re-infection.
In addition, as I said, no one yet knows how long the immune system remains after an infection. And what kind of immune memory is it – cellular, humoral? Serological testing (testing for antibodies) allows you to understand only that in the next two months you are protected from infection. But in order to understand more distant prospects, we must wait for the results of research.
– Now there is a lot of talk about the threat of the "second wave" of the epidemic. Do you think we still have a chance that immunity against the "crown" will be long-lasting?
Alexander Gorelov: I think it is hardly possible to count on the formation of a stable, long-term immunity to the coronavirus. This is not measles, not mumps, not rubella, having been ill once, most people acquire immunity for the rest of their lives. Unfortunately, for respiratory infections, including influenza, this is a classic example, even after vaccination, immunity is not preserved for more than six months. The new coronavirus is also a respiratory infection. We have yet to find out how long the immunological memory will be for him.
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