Until now it was thought that the antibody tests allow high accuracy to identify people, already ill COVID-19. However, recent studies suggest otherwise.
Sore throat, cough and a slight fever? Maybe we should have a test for the coronavirus SARS-CoV-2? In recent months this idea attends almost every one, there are the typical cold symptoms. To check whether a person is infected with at the moment and if he can infect others, mainly applied in the PCR test, carried out by the method of polymerase chain reaction. In this case, the patient with a cotton swab taken from the throat sample of saliva.
What if the person already had COVID-19 and didn’t even notice, because many disease are asymptomatic? In order to identify the presence of infection in the past, doctors use a different method – the so-called serological test (ELISA). It shows the presence of antibodies that have developed immune system in combating the virus.
Why do we need antibody tests?
For the test ELISA the patient take a drop of blood is placed in a special container and mixed with the reagent. If the sample is colored in a different color, it is, in principle, means that a person is already ill and he has formed an immunity. The presence of antibodies does not exclude the risk of re-infection of SARS-CoV-2, but its probability ten times lower than that of people who have antibodies have not been identified.
Serological tests allow us to ascertain how many people had COVID-19 asymptomatic or mild symptoms, and is it enough for the formation of collective immunity. It can help politicians to take the right steps to lift restrictions imposed in connection with the pandemic
Is immunity to the coronavirus?
However, how such tests are accurate and whether they all recover from COVID-19 create immunity? The answers to these questions tried to find scientists of the University of Lübeck. Most of the people who participated in their study had COVID-19 in mild or moderate form.
However, scientists were unable to detect antibodies in the blood to about one quarter of patients, in spite of earlier diagnosis and the expressed symptoms COVID-19.
But in the blood of two of the ten patients who recover from COVID-19 asymptomatic, was detected a high concentration of antibodies. This raises not only the question of whether produced from all infected COVID-19 immunity, but can I use of antibody tests to identify the real number of survivors.
How accurate are antibody tests?
It is believed that to obtain reliable serologic test result, since the coronavirus must pass up to four weeks: during this time, antibodies should be produced in the body in sufficient quantity. It is however only the estimated time. In some patients antibodies are actively produced almost immediately following infection, while others, apparently, they do not appear, despite the detection of coronavirus them in the active form.
In addition, in some cases a positive diagnosis can be made to a person who is ill with other coronavirus infections, but not COVID-19. In countries with a low number of cases per capita, the error test will be higher than in countries where a significant proportion of people already infected with coronavirus.
For example, if a country has infected half of the population of 50 patients with a positive test result only one will be delivered to the wrong diagnosis. If the country has infected only one person in a thousand, in nine of the ten positive samples actually no antibodies COVID-19. German doctors stress that in some cases, inaccurate test results can lead to undesirable consequences. In particular, patients who erroneously says that they have detected antibodies to COVID-19, will assume that they can not re-infected by a virus or spread it to others.
Immunity to coronavirus: more questions than answers
China also actively conducted studies of the antibody tests. Local scientists are trying to figure out how long a person remains immune to the coronavirus. The study, published in the scientific journal Nature, the scientists compared the patients who had COVID-19 asymptomatic and those with symptoms were observed. It turned out that the immune system asymptomatic patients reacted to the pathogen is less active.
The results of the study also showed that after three months the level of antibodies in the blood of people who have had COVID-19 asymptomatic, was close to zero. So the simple answer to the question, is all infected COVID-19 immunity is not yet possible. Unknown is what should be the level of antibodies in the body that a person could not re-infected by the coronavirus itself or be a source of infection for others.