Newborn Jaundice: Why It Is Not Caused by the Hepatitis B Vaccine

Most parents encounter jaundice during their baby’s first days or weeks of life. A yellowish tint to the skin or the whites of the eyes can be worrying, so it is natural to ask: why did this happen?

The hepatitis B vaccine is sometimes blamed because it is given shortly after birth, and many babies develop jaundice afterwards. The logic may seem simple: the baby received a vaccine and then turned yellow. But timing alone does not prove causation.

To understand why newborn jaundice is generally unrelated to hepatitis B vaccination, it is important to first understand what causes the yellow colour in the first place.

The cause of jaundice: bilirubin

Red blood cells are constantly being replaced in the body. When older red blood cells break down, haemoglobin is released and eventually converted into bilirubin.

Initially, bilirubin is present in its unconjugated, or indirect, form. This form is poorly soluble in water and, at sufficiently high levels, can be toxic. The liver processes bilirubin and converts it into conjugated, or direct, bilirubin, which can then be excreted in bile and eliminated through the intestines.

Total bilirubin is the combined amount of direct and indirect bilirubin in the blood. When bilirubin levels rise enough to cause visible yellowing of the skin or the whites of the eyes, this is called jaundice.

Jaundice itself is not a diagnosis. It is a sign that can have different causes.

Why bilirubin levels can increase

There are three main mechanisms. First, too much bilirubin may be produced. This can happen when red blood cells are broken down more rapidly than usual. Second, the liver may not be able to process bilirubin quickly enough. This can occur because of liver disease, but it can also result from the normal functional immaturity of the newborn liver.

Third, the flow of bile may be impaired, preventing conjugated bilirubin from being excreted normally. This is why the statement “jaundice means the liver is damaged” is not always correct. Bilirubin levels can increase even when the body is going through normal physiological processes.

What happens in newborns

Several factors naturally contribute to higher bilirubin levels after birth. Newborns undergo rapid changes in their blood and circulation, including the breakdown of red blood cells. At the same time, the liver's enzyme systems are still developing and may not process bilirubin as efficiently as those of an older child or adult. Some bilirubin can also be reabsorbed from the intestines.

As a result, physiological jaundice is extremely common in newborns. Clinical jaundice develops in approximately 60% of full-term and 80% of preterm newborns. It usually appears after the first 24 hours of life, becomes more noticeable over the following days, and then gradually resolves.

This is also the period when newborns may receive their first medical interventions, including hepatitis B vaccination. But two events occurring around the same time does not mean that one caused the other.

Physiological jaundice is not a contraindication to vaccination

In most newborns, elevated bilirubin is part of the normal adaptation to life outside the womb. Physiological jaundice requires appropriate observation and assessment, but it is not, by itself, a contraindication to hepatitis B vaccination.

The same applies to certain other benign causes of prolonged unconjugated hyperbilirubinaemia, including breast milk jaundice.

Breast milk jaundice

In some babies, jaundice can persist longer than usual. One possible explanation is breast milk jaundice. It typically appears or becomes more noticeable after the first week of life and may persist for several weeks.

The baby is otherwise generally well and continues to grow and feed normally. Breast milk jaundice is associated with differences in bilirubin metabolism and does not usually require stopping breastfeeding. It is also not, by itself, a contraindication to vaccination.

Jaundice associated with insufficient milk intake

This should not be confused with breast milk jaundice. If a newborn receives insufficient amounts of milk during the first days of life, bilirubin levels may rise because bilirubin is not being eliminated effectively. In this situation, it is important to assess feeding, the number of feeds, weight loss and the baby's overall condition.

The solution is not to stop breastfeeding, but to identify the reason for insufficient milk intake and improve feeding. Again, this does not mean that a vaccine caused the jaundice.

When jaundice requires medical attention

Not all jaundice should automatically be considered physiological. Jaundice requires careful medical assessment when it:

• appears within the first 24 hours after birth;
• increases rapidly;
• is accompanied by signs of illness or deterioration in the baby's condition;
• persists longer than expected;
• is associated with significantly elevated bilirubin levels;
• involves elevated direct bilirubin or signs of impaired bile flow.

In these cases, possible causes may include haemolytic disease, infections, inherited metabolic disorders, liver disease, biliary disorders and other conditions.

A bilirubin level alone does not always identify the cause. Assessment may take into account the baby's age in hours or days, bilirubin levels and trends, the proportion of direct and indirect bilirubin, gestational age, feeding, weight loss and the baby's overall condition.

What about vaccination?

This is where it is important to distinguish physiological jaundice from serious illness. Ordinary physiological jaundice does not mean that a newborn cannot be vaccinated.

If a baby has a serious illness or an unstable clinical condition, the timing of vaccination may need to be considered individually. But the fact that a baby develops jaundice after vaccination does not mean that the vaccine caused it.

Jaundice is extremely common during the same period of life when hepatitis B vaccination is often given. This makes it easy to mistake a temporal association for a causal relationship.

“After this” does not mean “because of this.”

Gilbert syndrome and vaccination

One possible cause of elevated unconjugated bilirubin is Gilbert syndrome, an inherited condition associated with reduced activity of an enzyme involved in bilirubin conjugation. Gilbert syndrome itself is generally not a contraindication to vaccination.

The key point

Jaundice is common in newborns, and in most cases it is part of the body's normal adaptation after birth. Newborns naturally experience increased red blood cell breakdown while their bilirubin-processing systems are still maturing. These processes occur regardless of whether the baby has received a hepatitis B vaccine.

That is why jaundice appearing after vaccination does not, by itself, demonstrate that the vaccine caused it.

At the same time, jaundice should not be assessed by appearance alone. Some forms require investigation and treatment, so jaundice that appears very early, increases rapidly or is accompanied by a worsening of the baby's condition should be evaluated by a healthcare professional.

Physiological jaundice is not a reason to refuse vaccination. Pathological jaundice, however, must be recognised and treated promptly — regardless of whether a child has been vaccinated or not.