The hepatitis B (Hep B) vaccine is given at birth to protect babies from a virus that can cause lifelong liver disease, including cirrhosis and liver cancer, if they are infected early in life. Newborns and young infants who catch hepatitis B are much more likely than adults to become chronically infected, so early vaccination is a critical “safety net.”
Preventing infection from birth parent
Hepatitis B can pass from an infected mother (or birth parent) to the baby during labor and delivery through contact with blood and body fluids. Giving the vaccine within 24 hours of birth greatly reduces the chance of this perinatal transmission and is part of the recommended prevention strategy worldwide.
Protecting against hidden exposures
Many adults with hepatitis B do not know they are infected and can spread the virus without symptoms, so relying only on known risk factors or test results misses some infected caregivers. A universal birth dose protects babies not only from their mothers but also from infected family members or other contacts in the household during early infancy.
Lowering lifelong disease risk
If infection happens in the first year of life, around 90% of babies will develop chronic hepatitis B, which can later lead to liver failure and liver cancer. Vaccinating at birth, then completing the series, prevents most of these chronic infections and has already led to major reductions in hepatitis B disease in children.
Long-lasting immunity
Health organizations recommend that all babies receive a birth dose followed by additional doses in infancy, which provide strong, long-lasting protection for decades, often into adult life. High coverage with a timely birth dose plus the full series is projected to prevent hundreds of thousands of deaths from hepatitis B in children born over current decades.
Why not wait until later?
Because early-life infection is the most dangerous and often silent, delaying the first dose until weeks or months after birth leaves a window of vulnerability when exposure can already occur. The birth dose closes this gap, acting as an immediate shield in the first days of life while the rest of the vaccine series builds full immunity.
