New data support the hope that vaccinated and recovered people, in an average, disregarded the omikron variant less with an average. As a prop shows, so-called T cells in vaccinated and recovered react as much to omikron as to older variants. These immune cells can combat the new variant - while antibodies from vaccinations or an infection with an earlier variant protect only a little. After a disease or vaccination, the T cells usually remain longer than antibodies and play the key role when protection against a difficult course.
The group led by Catherine Riou and Wendy Burgers from the University of Cape Town searched blood samples from 70 vaccinated and recovered patients for evidence of two types of T cells: those with CD8 receptors, which destroy infected cells, and those with CD4 receptors, which stimulate the production of antibodies. For this purpose, the researchers brought cell cultures of people who had been vaccinated or recovered about one and a half months ago into contact with the characteristic antigens (surface proteins) of various virus variants.
In 70 to 80 percent of the cases, the hoped-for T cell response could be observed on Omikron-similar to the older variants Beta and Delta. Up to a month after the vaccination, the answer was even observed in 85 percent of the cases. The specific T cells of the vaccinated and recovered recognized Omikron almost as well as the original Wuhan variant, according to the group. And this T cell immunity contributes to protection against heavy covid-19.
T cells' function in the immune system
T-cells form the acquired immune response together with B cells and the antibodies they produce. The T cells are white blood cells that recognize non-body structures such as pathogens on certain characteristics, the antigens. They search for the bodies for those cell changes to which they were trained like a guard patrol. There are guards who kill an infested cell themselves: the T killer cells with so-called CD8 receptors (T cells with the molecule CD8 on the surface). The T-helper cells with CD4 receptors do not intervene themselves, but get help: They stimulate the B cells for the formation of tailor-made antibodies via messenger substances. These bind to the antigens of the virus and thus initiate its end.
In addition, regulatory T cells ensure that their colleagues do not also destroy healthy body cells. Such overshooting attacks could be responsible for severe courses of Covid-19, as a German research team showed. The group detected increased T cells with CD16 receptors in seriously ill and deceased Covid patients. Actually, T cells are only directed against affected or altered body cells, explains immunologist Birgit Sawitzki in a press release from the Charité. However, activation via CD16 overrides the safety mechanism, and so even uninfected vascular cells can be attacked.
Omikron circumvents part of the vaccination protection
Since November, the Omykron variant has become increasingly popular in many countries. Figures from Denmark, for example, showed that the vaccine effectiveness, measured by protection against infection, against Omikron immediately after the first vaccination with BioNTech was significantly lower at 55 percent than against the Delta variant – and also fell quickly.
A British study was no longer able to demonstrate vaccination protection around four months after the second vaccination with AstraZeneca; Biontech was still given around 35 percent. After a Biontech booster, protection doubled by antibodies. A study by the University of Göttingen also came to similar results. How long the effect of the third dose lasts is still unclear.
A survived disease apparently protects more permanently against a new infection, as recently suggested a study from Israel. Although the protection against infection also disappeared over time in recovered patients, it remained at a higher level than after two doses of vaccine: Those who were vaccinated twice had an approximately eight times higher risk of infection than a recovered person half a year later. A fresh booster reduced the risk to a tenth. However, the best protection had convalescents who were vaccinated after surviving the disease.
