Two Different Vaccines Have Been Developed That Protect Vaccinated Individuals

Two different vaccines have been developed that protect vaccinated individuals against pneumococcal disease, a bacterial infection that causes pneumonia, meningitis and sepsis (blood stream infection) . This disease is caused by the bacteria, Streptococcus pneumoniae. One vaccine, PPSV23, is a mixture of polysaccharides isolated from 23 different serotypes of S. pneumoniae. The second vaccine, PCV13, is a conjugate vaccine made from polysaccharides of 13 different serotypes of the bacteria conjugated to diphtheria toxoid (inactivated toxin protein) . The PPSV23 vaccine is only given to adults, whereas infants and small children are given PCV13. This is because:

A) Adults are likely exposed to more different strains (serotypes) of S. pneumoniae than infants.
B) Adult B cells don't require T_FH cells to make antibody responses.
C) Infant B cells are immature and don't respond to TI-2 antigens.
D) Adult B cells respond more robustly than infant B cells to B-cell mitogens.
E) Infant B cells are more dependent on the cytokine BAFF.