Most Covid cases are not found with antibody tests

Every person who has come into contact with the coronavirus produces antibodies. These antibodies can be detected in a blood test. In this way it can be estimated how many infected people there were.

However, immunologists at the University of Zurich have now found that if the course of the disease is mild, there are hardly any antibodies in the blood, the daily newspaper writes. Since more than 80 percent of the Covid 19 cases are mild, this could indicate a significantly larger number of unreported cases than previously assumed.

The team led by Onur Boyman, professor at the Clinic for Immunology at the University Hospital in Zurich, had examined two different groups. One that consisted of patients with mild or severe disease, and one with health workers who came into contact with the virus.

An estimated five times more infected than previously thought

The researchers then searched for antibodies, not only with common antibody tests, but also in the eyes, nose and mouth. “The usual antibody tests do not cover all cases,” study leader Boyman told the Tagesanzeiger. It can therefore be assumed that up to five times as many people came into contact with the corona virus as was previously assumed.

“This is an interesting study,” says Daniel Pinschewer, who heads the Department of Experimental Virology at the Department of Biomedicine at the University of Basel. “I find it plausible that with today’s blood antibody tests we cannot detect all of the infections that have survived.”

Antibodies are different

In the case of an infection, different antibodies such as IgM, IgA or IgG are formed. These have different abilities, occur at different stages of the infection, and especially in different places in the body.

If an infection is imminent, the IgM antibodies first appear. Although they are difficult to penetrate into the tissue due to their size, they can also block a larger amount of viruses.

IgA antibodies bind more strongly and are mainly found in the mucous membranes. According to the study, they appear in mild cases around eight days after the onset of symptoms and can only be detected temporarily in the blood in a small part of the cases.

IgG are the least common and can be anywhere in the body. Although they have been detectable for the longest time, they have mostly not been found in the blood of infected people with a mild course.

Antibodies to Covid-19 in the mucous membranes

However, the researchers found IgA in the nasal mucosa of mildly ill people and health workers. This even in people who showed no symptoms. This was the first time that it could be demonstrated that Covid 19 patients have antibodies in the mucous membranes. Antibodies could only be detected in the blood of the seriously ill.

In addition to the antibodies, there are also the T lymphocytes. You fight a virus if it is already in the body’s cells. In addition, they have a kind of memory and thus remember an illness they have already gone through. Anyone who carries the T lymphocytes in the body after an infection no longer has any detectable antibodies in the blood.

Nevertheless, there could be at least partial immunity. “This is a fascinating study,” Francois Spertini, professor of immunology at the University Hospital Lausanne CHUV, told the Tagesanzeiger. “It helps us explain why so few people have antibodies in their blood and why these values ​​are probably misleading.”

Children and Covid-19

Children rarely develop the new type of corona virus. The study also provides certain clues to this riddle. “Because children often suffer from upper respiratory tract infections, they may have protective IgA antibodies in the mucous membranes,” the authors write. These antibodies could be due to a fitter immune system in the mucous membranes and therefore offer some protection. “That could explain, among other things, why children rarely fall ill.”

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.