**Core Concept**
The concept of a "zero dose" of polio vaccine refers to the administration of the first dose of the inactivated poliovirus vaccine (IPV) or the oral poliovirus vaccine (OPV) at birth, as part of a strategy to prevent poliomyelitis. This approach aims to provide early protection against poliovirus infection and reduce the risk of polio outbreaks.

**Why the Correct Answer is Right**
The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) recommend administering the first dose of IPV or OPV at birth, as part of a routine vaccination schedule. This early vaccination helps to establish a strong immune response against poliovirus, reducing the risk of polio transmission and disease. The "zero dose" is typically administered at birth, before the infant is discharged from the hospital.

**Why Each Wrong Option is Incorrect**
**Option A:** There is no established "first dose" of polio vaccine that is administered at a specific age other than the zero dose.
**Option B:** The "second dose" of polio vaccine is typically administered at 4-6 weeks of age, not at birth.
**Option C:** The "booster dose" of polio vaccine is not typically administered at birth, but rather as a booster shot at 4-6 years of age.

**Clinical Pearl / High-Yield Fact**
Administering the first dose of polio vaccine at birth can help to prevent polio outbreaks, particularly in areas where poliovirus transmission is high. This approach is a key component of global efforts to eradicate poliomyelitis.

**Correct Answer: B. First dose of OPV or IPV at birth.**