A young girl has had repeated infections with Candida albicans and respiratory viruses since the time she was 3 months old. As pa of the clinical evaluation of her immune status, her responses to routine immunization procedures should be tested. In this evaluation, the use of which of the following vaccines is contraindicated?

**Core Concept**
The use of certain live vaccines in immunocompromised patients can pose a risk of vaccine strain infection. In this case, the patient's repeated infections with Candida albicans and respiratory viruses suggest an impaired immune system, necessitating careful consideration of vaccine selection.

**Why the Correct Answer is Right**
BCG (Bacillus Calmette-Guérin) vaccine is a live attenuated vaccine used to protect against tuberculosis. In immunocompromised individuals, such as those with severe combined immunodeficiency (SCID) or other primary immunodeficiencies, live vaccines can cause vaccine strain infection, leading to severe disease. This is because these individuals lack the necessary immune function to control the replication of the attenuated vaccine strain.

**Why Each Wrong Option is Incorrect**
**Option A:** Diphtheria toxoid is a killed vaccine, which is safe for use in immunocompromised individuals. It does not pose a risk of vaccine strain infection.
**Option B:** Bordetella pertussis vaccine is a component of the combined diphtheria, tetanus, and pertussis (DTP) vaccine, which is also a killed vaccine. It is safe for use in immunocompromised individuals.
**Option C:** Tetanus toxoid is a killed vaccine, which is safe for use in immunocompromised individuals. It does not pose a risk of vaccine strain infection.

**Clinical Pearl / High-Yield Fact**
Immunocompromised patients should receive killed or subunit vaccines, rather than live attenuated vaccines, to minimize the risk of vaccine strain infection. This includes patients with primary immunodeficiencies, HIV/AIDS, or those undergoing immunosuppressive therapy.

**Correct Answer:**
✓ Correct Answer: D. BCG.

✓ Correct Answer: D. BCG