The hepatitis B vaccine is given at birth primarily to prevent newborns from acquiring hepatitis B infection from their mother during delivery. Newborns infected with hepatitis B at birth have a 90% chance of developing chronic hepatitis B, which can lead to serious liver diseases such as cirrhosis and liver cancer later in life. Since many mothers may not know their hepatitis B status or may have inaccurate test documentation, giving the vaccine at birth acts as a crucial safety net against perinatal transmission. The vaccine also protects infants from hepatitis B infection through contact with other carriers after birth. Administering the vaccine within 24 hours of birth has been shown to be highly effective in preventing infection and is a cornerstone of hepatitis B prevention policies worldwide.