**Question:** The 23 valent pneumococci vaccine is recommended in all except

A. Children under 2 years old
B. Pregnant women
C. Patients with compromised immune system
D. Patients with allergy to the vaccine or its components

**Core Concept:**
The 23-valent pneumococcal polysaccharide vaccine (PPV23) is a pneumococcal vaccine that provides immunity against 23 different serotypes of Streptococcus pneumoniae, which are the causative agents of various respiratory infections. PPV23 is generally safe and effective, but its immunogenicity is generally lower in certain high-risk populations.

**Why the Correct Answer is Right:**
The correct answer, "Children under 2 years old," is based on the fact that infants and young children have immature immune systems that may not respond adequately to the vaccine. This age group is more susceptible to pneumococcal infections and would therefore require other vaccination options, such as the pneumococcal conjugate vaccine (PCV13) which is better suited for this age group.

**Why Each Wrong Option is Incorrect:**
A. **Pregnant women**: Although PPV23 is generally safe during pregnancy, it is recommended to avoid giving the vaccine during the first trimester to prevent any potential adverse effects on the developing fetus. In the second and third trimester, PPV23 can be given, but alternatives like PCV13 are preferred due to the potential risk of fetal exposure.

B. **Patients with compromised immune system**: PPV23 is generally contraindicated in individuals with a compromised immune system due to the vaccine's inability to provide adequate protection in these patients. Therefore, alternative vaccines like PCV13 are recommended in such cases.

C. **Patients with allergy to the vaccine or its components**: PPV23 is generally contraindicated in patients with a history of severe allergic reactions to the vaccine or its components. In such cases, alternative vaccines like PCV13 are recommended.

D. **Patients with a history of previous pneumococcal infection**: PPV23 can be given to patients with a history of pneumococcal infection, as it provides immunity against additional serotypes. However, for patients with a history of severe pneumococcal disease, other vaccines like PCV13 are preferred due to the higher risk of severe disease.

**Clinical Pearls:**
1. When considering vaccination for infants and pregnant women, PCV13 is preferred over PPV23 due to potential risks and better immunity provided.
2. In patients with compromised immune systems, alternative vaccines like PCV13 are recommended as PPV23 may not provide adequate protection.
3. For patients with a history of severe pneumococcal disease, PCV13 is preferred over PPV23 due to the higher risk of severe disease caused by the additional serotypes in PCV13.
4. Patients with a history of previous pneumococcal infection can receive PPV23, as it provides immunity against additional serotypes, but for patients with severe pneumococcal disease, PCV13 is preferred due to the