Hepatitis B is a serious viral infection that primarily targets the liver, capable of causing both acute and chronic disease. This article explains why the Hepatitis B vaccine is administered to infants immediately after birth to provide early protection against this potentially devastating illness.
What is Hepatitis B
Hepatitis B is caused by the Hepatitis B virus (HBV), which leads to inflammation of the liver. The infection can manifest as an acute, short-term illness, or it can progress to a serious, long-term chronic condition. Chronic HBV infection can result in significant liver damage over time, including cirrhosis, a severe scarring of the liver, and hepatocellular carcinoma, a type of liver cancer.
The Hepatitis B virus is highly contagious. Worldwide, an estimated 254 million people were living with chronic hepatitis B infection in 2022, with approximately 1.1 million deaths attributed to the disease, primarily from cirrhosis and liver cancer.
How Infants Acquire Hepatitis B
The primary way infants acquire Hepatitis B is through perinatal transmission, which occurs when an infected mother passes the virus to her baby during pregnancy or, more commonly, during the birthing process. This transmission route is responsible for a significant proportion of chronic HBV infections globally.
Many mothers infected with Hepatitis B may not exhibit symptoms, making them unaware they carry the virus. This asymptomatic nature means that universal screening and vaccination strategies are necessary to protect newborns. Without intervention, a mother who is positive for Hepatitis B surface antigen (HBsAg) carries a risk of transmitting the infection to her offspring at birth.
Why Immediate Vaccination is Crucial
Immediate vaccination at birth is important because infants infected with Hepatitis B during the perinatal period face a very high risk of developing chronic infection. Approximately 90% of infants who acquire HBV at birth will develop a lifelong chronic infection, a rate significantly higher than the 5% to 10% seen in adults. This early chronic infection often remains asymptomatic for many years, silently progressing to severe liver damage later in life.
The newborn’s immune system is not fully developed, making them less capable of clearing the virus compared to older children or adults. This vulnerability means that the virus can establish itself firmly in the infant’s body, leading to liver disease, liver failure, and liver cancer decades later. The birth dose of the Hepatitis B vaccine helps prevent the virus from establishing a chronic infection immediately after potential exposure during birth.
For infants born to mothers with known or suspected Hepatitis B infection, the vaccine is often administered alongside Hepatitis B Immune Globulin (HBIG). HBIG provides immediate, short-term protection by supplying antibodies to fight the virus, acting as a bridge until the baby’s immune system can respond to the vaccine and produce its own antibodies. This combined approach is highly effective, with studies showing up to 94% efficacy in preventing perinatal transmission when both are given within 12 hours of birth. Even if HBIG is not given, the birth dose of the vaccine alone is 75% effective in preventing transmission.
Safety and Efficacy of the Birth Dose
The Hepatitis B vaccine is considered very safe for infants, including newborns. Extensive testing has confirmed its safety and efficacy, with over a billion doses administered worldwide. The vaccine contains only a small, non-infectious part of the Hepatitis B virus protein and cannot cause the disease itself.
Side effects in newborns are typically mild and temporary, such as soreness, redness, or swelling at the injection site. Some infants may experience headache, fever, or fatigue, but serious adverse events are rare. The vaccine does not overwhelm a baby’s developing immune system; it introduces a small component for the immune system to recognize and build protection against.
When administered as part of the recommended series, beginning with the first dose at birth, the Hepatitis B vaccine is highly effective in preventing infection. After completing the full series, typically three to four doses, approximately 98% of healthy full-term infants achieve immunity to the virus. This high rate of protection provides long-term immunity, likely lasting for life, significantly reducing the risk of chronic infection and its severe health consequences.