**Core Concept:** Prevention of neonatal hepatitis B infection

Hepatitis B virus (HBV) infection is a significant public health concern, leading to chronic liver disease and liver cancer. In pregnant women, HBsAg positivity indicates HBV infection and poses a risk to the newborn. Prevention measures include administering the hepatitis B immunoglobulin (HBIG) and the hepatitis B vaccine to the newborn within 12 hours of birth.

**Why the Correct Answer is Right:**

1. **Option A (HBIG):** Hepatitis B immunoglobulin is a polyclonal antibody preparation targeting HBsAg, inhibiting viral entry into the newborn's hepatocytes. By blocking HBsAg binding, HBIG prevents the virus from replicating within the liver cells and reduces the risk of vertical transmission to the newborn.

2. **Option B (Vaccine):** Hepatitis B vaccine is a recombinant DNA vaccine composed of surface antigens (HBsAg). It stimulates the newborn's immune system to produce HBsAg-specific antibodies, providing immunity against future HBV infections.

3. **Option C (Neither):** Neither HBIG nor vaccine administration does not protect the newborn from HBV infection, leading to a high risk of vertical transmission.

4. **Option D (Both):** Administering both HBIG and vaccine to the newborn within the first 12 hours of life significantly reduces the risk of HBV infection, making it the correct answer.

**Why Each Wrong Option is Incorrect:**

1. **Option C (Neither):** Not administering any preventive measures increases the risk of vertical transmission, making it an incorrect choice.

2. **Option D (Both):** While administering both HBIG and vaccine is essential, the timing of administration is crucial. Administering them at a later time does not have the desired effect and thus remains incorrect.

**Why Option D is Right:**

The correct timing for administering HBIG and vaccine is within the first 12 hours of life. This critical window ensures that the newborn's immune system receives the necessary stimulation to produce HBsAg-specific antibodies and develop immunity against HBV infection.

**Clinical Pearls:**

1. **Hepatitis B vaccine:** The Hepatitis B vaccine is one of the most successful vaccines in preventing viral infections, with a high immunogenicity rate. It was approved by the FDA in 1982 and later recommended for routine vaccination of infants.

2. **Hepatitis B immunoglobulin (HBIG):** Administered within 12 hours of life, HBIG binds to HBsAg in the mother's blood, preventing the virus from entering the newborn's hepatocytes, reducing the risk of vertical transmission by up to 95%.

In conclusion, administering HBIG and vaccine together within the first 12 hours of life is crucial to provide protection against vertical transmission of HBV.