Which type of immunity is acquired when an individual's immune system is exposed to a pathogen through vaccination or natural infection?

Explanation: T cells are a type of lymphocyte that plays a central role in cell-mediated immunity. They can recognize and destroy abnormal cells, including cancer cells, through direct cell-to-cell interactions.

Incorrect choices:

b. B cells produce antibodies in response to specific pathogens, but they do not directly attack cancer cells.

c. Antibodies are protein molecules that can bind to specific antigens on pathogens, but they do not have a direct role in attacking cancer cells.

d. Macrophages are phagocytic cells that engulf and destroy foreign substances, including pathogens, but they are not the primary cells responsible for recognizing and attacking cancer cells.

Explanation: The pneumococcal polysaccharide vaccine is recommended for older adults to protect against pneumonia caused by Streptococcus pneumoniae bacteria. The influenza vaccine is recommended annually for people of all ages to prevent the flu.

Incorrect choices:

a. The hepatitis B vaccine is not specifically recommended for older adults to prevent pneumonia.

b. The influenza vaccine protects against the flu, not pneumonia.

d. The HPV vaccine is recommended for adolescents and young adults, not older adults, and does not protect against pneumonia.