Vaccine of yellow fever is
**Core Concept**
The yellow fever vaccine is a live, attenuated vaccine that provides long-term immunity against yellow fever virus. It is a crucial tool in the prevention of yellow fever, particularly in areas where the disease is endemic.
**Why the Correct Answer is Right**
The yellow fever vaccine contains a weakened form of the yellow fever virus, known as the 17D strain. When administered, this vaccine stimulates the body's immune system to produce antibodies against the virus, providing protection against infection. The vaccine is typically given as a single dose, and immunity is expected to last for life. The vaccine's effectiveness is due to the presence of the envelope protein E, which is a key antigen in the yellow fever virus.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the yellow fever vaccine is not a killed-virus vaccine, which would not provide live immunity.
**Option B:** This option is incorrect because the yellow fever vaccine is not a subunit vaccine, which would only provide protection against specific components of the virus, not the entire virus.
**Option C:** This option is incorrect because the yellow fever vaccine is not a conjugate vaccine, which is typically used for diseases such as pneumococcal disease.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the yellow fever vaccine is not recommended for individuals with certain medical conditions, such as a history of thymus disease or immunodeficiency.
**Correct Answer: C. 17D strain**