All are true regarding Hib vaccine except:
**Core Concept**
The Hib vaccine is a conjugate vaccine designed to protect against invasive Haemophilus influenzae type b (Hib) infections, a leading cause of bacterial meningitis and other serious diseases in young children. The vaccine works by inducing immune responses against the Hib capsular polysaccharide, a key virulence factor of the bacterium.
**Why the Correct Answer is Right**
The Hib vaccine is typically administered in a series of doses, starting at 2, 4, and 6 months of age, with a booster dose at 12-15 months. This schedule is designed to provide early protection against Hib infections and to maintain immunity through childhood. The vaccine is highly effective in preventing invasive Hib disease, including meningitis, septicemia, and epiglottitis, and has greatly reduced the incidence of these conditions in countries where it has been widely used.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the Hib vaccine does not induce immunity against other strains of Haemophilus influenzae, such as non-typeable H. influenzae, which is a common cause of respiratory tract infections.
**Option B:** Incorrect because the Hib vaccine is not effective against Hib infections that have already occurred; it is intended to prevent new infections from occurring in individuals who have not yet been exposed to the bacterium.
**Option C:** Incorrect because the Hib vaccine is not a live vaccine and does not contain any infectious material from the Hib bacterium; it is a killed-vaccine conjugate that contains only the polysaccharide capsule of the bacterium.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the Hib vaccine is a conjugate vaccine, which means it is made by attaching the Hib polysaccharide to a carrier protein, such as diphtheria toxoid. This conjugation process enhances the immune response to the polysaccharide, making the vaccine more effective and longer-lasting.
**Correct Answer:** A.