The topic of immunity after surviving a corona infection is a priority for research. How long does it last – and is that reliable? Two new studies have now come to the conclusion that protection against re-infection could even last for decades.
A study led by the La Jolla Institute for Immunology (LJI) in San Diego (California), in which the Austrian virologist and vaccine researcher Florian Krammer from the Icahn School of Medicine at Mount Sinai Hospital in New York was also involved, now gives hope. According to the analysis, even eight months after being infected with Sars-CoV-2, most of those who recovered had enough immune cells to fight off the virus and prevent illness. What makes the researchers confident is the fact that the slow breakdown of these cells suggests that they will stay in the body for a very long time.
The study, which is available at bioRxiv, a platform for studies that have not yet been published, has not yet undergone a peer review. But it is considered to be the most extensive of its kind to date. Shane Crotty, a virologist at La Jolla and one of the leaders of the study, told the New York Times: 19 to have to go to hospital or become seriously ill. “
In the meantime, fears had surfaced, initially supported by individual studies, that immunity to the Sars-CoV-2 virus would rapidly decrease, which would have meant that any vaccinations would have had to be repeated frequently. Apparently, however, the individual subjects who feared a second infection were not sick again, but simply had too few antibodies to blood to be permanently resistant from a symptom-free course.
The researchers also found that lung disease survivors who contracted the first Sars-CoV virus in 2003 still had important immune cells – so-called memory cells – 17 years after their recovery.
Immune cells communicate with each other
These immune cells obviously communicate with one another. “During the integrated investigation of the different antibodies,” the study says, “of the memory B cells, T cells, CD8 + T cells and CD4 + T cells, we found that every component of Sars-CoV-2 Immunity memory had different kinetics “.
The number of antibodies has decreased in some patients. But that alone is not decisive for immunity. Because although antibodies in the blood are necessary to prevent a second infection by blocking the virus – a phenomenon called sterile immunity – immune cells that “remember” the virus are more likely to be crucial in preventing severe disease.
“Sterile immunity is quite rare, this is not the norm”, said Alessandro Sette, Immunologist at the La Jolla Institute of Immunology and co-director of the study, The New York Times. It is more common, however, that people are infected a second time with a corresponding pathogen, the immune system recognizes the intruder and quickly stops the infection. The coronavirus is particularly slow and gives the immune system plenty of time to react. This also explains why the mean time for severe corona symptoms with a fatal course in immunocompromised patients is 19 days after infection.
Majority of the test persons had slight progressions
For people with a stable immune system, the following applies: “The virus can be dealt with so quickly that one neither develops symptoms nor is contagious,” says Sette. The research team examined 185 men and women between 19 and 81 years old, all of whom had recovered from Corona. The majority had only felt mild symptoms and did not have to go to inpatient treatment. Some had their blood drawn only once, and 38 subjects also submitted several samples over a period of several months.
The scientists focused on four components of the immune system: antibodies, B cells, which produce more antibodies than necessary, and CD8 + T cells and CD4 + T cells, which destroy other infected cells.
It turned out that although there were up to 200-fold fluctuations in the values among the test persons, the antibodies were stable and only decreased slightly six to eight months after the infection. While the T cells were also slowly decreasing, the B cells increased – why is still unclear.
It is just as difficult to predict how long a corona immunity could last. This is because the scientists do not yet know which levels of the various immune cells are necessary to protect against the virus. So far, however, according to the researchers, it seems that even a small proportion of antibodies or T and B cells could be sufficient to protect those who have survived an infection.
Second study supports immunity thesis
A second recently published study underpins the thesis of longer lasting immunity. It was carried out by researchers from Huazhong University in Wuhan, China, and the Institute of Virology at the University of Duisburg-Essen. There, too, the immune response of recovered persons was observed over a longer period of time. Wuhan was the starting point of the pandemic. A Sars-CoV-2-typical memory of the T cells lasts a long time in most of the test subjects, according to the scientists working with Prof. Jia Liu.
“To be located in Wuhan, where the pandemic broke out, puts us in a position to carry out the long-term analyzes of T memory cells for Sars-CoV-2 in convalescent Covid-19 patients,” it says at the beginning of the Study that can also be viewed on the bioRxiv preprint server. The result: “Sars-CoV-2-specific antibody reactions are rather short-lived – while the T-cell memory is more lasting.”