The defenses against corona quickly disappear from the blood

#Immunologie Represents against the new coronavirus disappear from the blood after a few months.This raises questions about the feasibility of group immunity and the functioning of vaccines.

The defense against the new coronavirus wears out quickly. The antibodies that humans produce when infected with SARS-COV-2 have sometimes disappeared from their blood within a few months, which may cause patients to be re-susceptible to Covid-19, according to a British study conducted in 65 COVID-19 patients in two London hospitals, Guy's and St. Thomas's Hospital. The manuscript describing the results came online this weekend, but has not yet been published in a scientific journal. It is the first time that the development of immunity in COVID-19 patients has been studied for a long time.

Sixty percent of participants started a strong antibody reaction that peaked in the three to four weeks after the first signs of disease. But two months later, only sixteen percent of patients had a lot of antibodies in the blood. In some people, the concentration had become twenty times less. The researchers want to follow the group even longer to see if the decline continues. The question is whether these recovered patients can regain Covid-19 because of the rapidly decreasing defenses. There are no indications for this yet, but it is something to take into account.

In any case, the outcome of the investigation leaves the hope of group immunity as a protection against the epidemic. According to experts, group immunity is achieved when two-thirds of the population have defenses against the virus; then there are so many people who are no longer susceptible to the virus that will extinguish an epidemic. But if people quickly lose their resistance again, building group immunity against SARS-COV-2 is unfeasible.

More severe infection
In London, it is estimated that 13% of the population have antibodies to SARS-COV-2, the highest rate in the whole of Britain. In the Netherlands, according to the latest measurement, the percentage of people with immune substances is 5.5 percent, with outliers reaching almost ten percent in parts of Brabant and Limburg. So far, there are no signs that immunity is diminishing in the population.

The UK study confirms the earlier finding that seriously ill COVID19 patients have a higher concentration of antibodies in the blood. However, it is not clear whether that is a reaction of the body to a more serious infection, or whether the high response with antibodies contributes to the aggravation of the disease.

The fact that human defenses can indeed quickly 'forget' the infection with a coronavirus — which allows the virus to strike again — is confirmed by a recent Amsterdam study. In it, the researchers looked at how often ten volunteers became infected with one of the four seasonal coronaviruses in ten years. Unlike SARS-COV-2, these are mild coronaviruses that generally cause only colds. There were big differences: some had to deal with infection three times in ten years, others 22 times. This had to do with how often a person accidentally came into contact with a virus, but also with how quickly immunity disappeared.

“We saw that people soon became susceptible again, sometimes after a year they reinfected with the same virus,” says doctor-researcher Arthur Edridge of the AMC in Amsterdam, first author of the article. “Because this applies to all four seasonal coronaviruses, which are genetically different and each has different points of contact in the body, we do not expect Covid-19 to be different.”

The main question then is whether the infection proceeds milder at the second or third time. There is no reliable judgment on this yet, says Edridge. “In our research, the number of participants was too small.” The relatively rapid disappearance of antibodies can also play off the coronavaccins that are now being developed in a hurry. Perhaps it will soon prove necessary to re-vaccinate people annually or even half-yearly for good protection.

Therefore, immunologists point out that a vaccine should not only stimulate the production of antibodies against the coronavirus, but also activate the defenses by white blood cells. The immune system fights viruses in two ways: with antibodies and cells. Without these cellular defenses, the defense against the virus is not complete, and is now increasingly evident.

An Australian study published on Monday in the trade journal Nature Medicine shows that COVID patients do not only produce antibodies against the virus during infection, but also a number of specific immune cells. The Australians then showed that among the 41 patients examined there were significant differences in the amount and strength of antibodies to the coronavirus, but that the 'aid' of immune cells ultimately determined the ability of the physical defenses to improve the Coronavirus harmless.

NRC Today