During the COVID 19 pandemic, the vaccination against SARS-CoV-2 did not offer optimal protection. However, a booster vaccination against the same variant or after another infection creates what is known as "hybrid immunity", which generates a much broader protective effect. The TWINCORE team, in cooperation with scientists from the Hannover Medical School and the German Primate Centre Göttingen, has now been able to show why this even protects against new virus variants with which the immune system had no previous contact, using samples from a patient. The patient was additionally vaccinated against SARS-CoV-2 months after recovering from COVID 19, and his antibodies were also able to inactivate new variants of the virus in the laboratory.
"This effect is based on a step in antibody maturation called somatic hypermutation," says Dr Matthias Bruhn, first author of the study and postdoctoral researcher at the Institute for Experimental Infection Research at TWINCORE. The B cell receptors change slightly due to individual somatic mutations that occur during the maturation of the antibodies. This diversification results in a mixture of different B cells. "According to previous doctrine, we would have expected somatic hypermutation to increase the affinity of the antibodies, in other words their binding strength to the antigen increases," adds Bruhn.