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They are seen as great hope in the fight against the crown crisis: the so-called antibody tests. They are intended to be used to assess on a large scale who has already had an infection with the novel coronavirus and, as a result, may have become immune. Many politicians and business representatives would like these people to be able to return to their jobs and normalize everyday life.
Scientists also hope that the test results provide information on how far society is from so-called collective immunity. The calculation is simple: if 60 to 70 percent of the population is infected with Sars-CoV-2, the virus could no longer spread due to the lack of contagion chains. Even if this condition is still a long way off, a large-scale study was started in Munich, which is supposed to provide at least clues to exactly this degree of infection with the help of antibody tests.
So far, however, all theories and approaches have had two crucial catch: on the one hand, whether immunity really exists after Covid disease 19 has not yet been adequately demonstrated. Therefore, the WHO recently warned about the called “immunity passports”. On the other hand, the testing procedure is not reliable enough.
Too many “false positive” signs
Antibody tests do not detect the pathogen itself, but antibodies, also called immunoglobulins, that the body produces in the course of infection to avoid the virus. Because the immune system does not produce so-called IgA antibodies until about a week after the onset of the disease, and long-term antibodies called IgG only several weeks later, the tests are, in principle, well-suited for testing for subsequent infection. .
However, a major disadvantage is that so-called cross-reactions can occur with other coronaviruses. Virologist Christian Drosten de Charité in Berlin said in an NDR podcast that almost all antibody tests give “false positive signals” if, for example, the patient has been infected with a cold coronavirus. Therefore, there is no certainty that if the test result was positive, there was actually an infection with Sars-CoV-2. And that can have dangerous consequences: if a test person mistakenly believes that they are immune to Sars-CoV-2 and can do without security measures, they are exposed to a considerable risk of infection.
Another problem is that the manufacturers of antibody tests have so far been able to certify their products themselves. According to one regulation, this is possible in the EU until May 2022. According to the federally owned Paul Ehrlich Institute, there has been a lack of generally recognized quality standards and testing by an independent body.
Only three antibody tests are reasonably useful
Because the situation in the USA USA It is similar, 50 scientists from various US universities. USA They took the initiative themselves and tested a total of 14 antibody tests to determine their reliability, including rapid tests and laboratory methods. A few days ago they published their result as a so-called preprint, which is not yet controlled by the scientific community. And the result is difficult: Thus, only three antibody tests were reasonably helpful.
Four of 14 products reported false positive results in 11 to 16 percent of cases. In other words, they feigned immunity that was not there. For most of the others, this was around five percent. And of the three highest-rated tests, two gave false positive results in one percent of cases and only one did not give any error results.
“These numbers are simply unacceptable,” Scott Hensley, a microbiologist at the University of Pennsylvania, told the New York Times. The proportion of people in the United States who have been exposed to the coronavirus is believed to be five percent or less. “If your test kit has a false positive of three percent, how do you interpret it? It is basically impossible. And if your kit gives false positive results of 14 percent, it is actually useless.” Hensley was not involved in the study.
To verify antibody testing, each product was evaluated with the same set of blood samples. This included samples from 80 people who had been shown to be infected with the novel coronavirus on several occasions, 108 samples from before the pandemic and 52 samples from people who tested positive for other viral infections but tested negative for Sars-CoV-2. been.
With its sobering results, the study dampens hopes for reliable knowledge of the population’s infection. Most of the tested products cannot be used to make reliable statements about immunity. At the same time, the research results also provide important clues about which antibody tests should be used in the future.
