**Core Concept**
Xavier and Yogender's infections are caused by different serogroups of Neisseria meningitidis, which is a leading cause of bacterial meningitis. The different serogroups have distinct polysaccharide capsules, leading to varying immune responses.

**Why the Correct Answer is Right**
Group B meningococcus (Neisseria meningitidis serogroup B) and Group C meningococcus (Neisseria meningitidis serogroup C) are two distinct serogroups of the same bacterium. The polysaccharide capsule of Group B meningococcus is different from that of Group C, which leads to different immune responses. This is why Xavier and Yogender's infections are caused by different serogroups. The immune response to one serogroup does not provide cross-protection against the other serogroup.

**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable, as this option is missing.
**Option B:** This statement might be true, but it's not the correct answer. To be sure, we need to evaluate the other options.
**Option C:** This statement might be true, but it's not the correct answer. To be sure, we need to evaluate the other options.
**Option D:** This statement is not true. There is no direct correlation between Xavier's infection and Yogender's infection, as they are caused by different serogroups of Neisseria meningitidis.

**Clinical Pearl / High-Yield Fact**
When treating bacterial meningitis, it's essential to identify the causative organism and its serogroup to choose the appropriate antibiotic therapy. Vaccines are available for some serogroups, such as Group C, but not for Group B.

**Correct Answer:** D.