COVID-19 immune response improves for months after vaccination At a Glance Researchers showed that B cells evolve after COVID-19 vaccination to help improve protection against SARS-CoV-2 over time. A better understanding of how the immune system responds to COVID-19 vaccination could lead to more effective and longer-lasting vaccination strategies. Antibodies are the immune system’s first line of defense against viruses like SARS-CoV-2.. Vaccines are the best way to protect yourself against COVID-19. They elicit a strong defense against SARS-CoV-2, the virus that causes the disease. Vaccines activate your body’s disease defense system, called the immune system. The response starts by engaging two kinds of immune cells: B cells, which produce antibodies that fight off the virus, and T cells, which destroy infected cells. After this initial response, levels of antibodies in the bloodstream begin to fall. But some B and T cells stay around to keep a “memory” of the virus and fight off fu