Read the following and answer the questions given below: In a study to test a new vaccine against a viral disease, mouse model testing is done. In this process, mice were vaccinated and their blood samples were tested. Mice developed mild disease symptoms. After few days those mice were again infected with the virus. This time they did not show any disease symptoms. Their blood samples were tested. Two graphs show antibody concentration for the first and second infection in mice blood. Based on the above information answer the following questions. How does vaccination work?

Options

A. The immune system produces antibodies which stay in the blood.
B. Memory lymphocytes remain in the body to fight off any future infection with the same pathogen.
C. The dead pathogen stays in the body and constantly stimulates the immune system.
D. All of these.

Answer

D