Hepatitis B vaccine Q&A: Why do babies need the shot?

The people at highest risk for contracting hepatitis B include health care workers, IV drug users and people having sex.

So why do babies get vaccinated for hepatitis B as soon as they are born? It’s a fair question, and health care providers have compelling answers. 

Hepatitis B is a virus that can do serious, sometimes fatal, liver damage. Although groups that are more exposed to swapping bodily fluids are at greater risk, anyone can get infected.

Getting infected with hepatitis B as a baby is extra dangerous. Infected infants have a 90% chance^[1] of developing the disease’s more dangerous chronic form. And a quarter^[2] of those babies will go on to die prematurely from the disease when they become adults, according to the American Academy of Pediatrics. 

When the vaccine was invented in the 1980s, doctors initially vaccinated only the highest risk individuals^[3]. Cases didn’t meaningfully decline^[4]. 

In 1991^[5], the Centers for Disease Control and Prevention began recommending vaccinations for everyone^[6] at birth. 

The protocol produced results^[7]: New infections dropped significantly^[8], especially among children and adolescents^[9].

“Now it’s a very uncommon disease in young children because of that vaccine,” Dr. Paul Offit, Children’s Hospital of Philadelphia pediatrician and infectious disease expert, said. “It was a remarkable, remarkable achievement.”

Today, infants get their first dose within 24 hours of birth and receive two to three more doses^[10] by the time they are 6 months old. 

But the CDC’s independent vaccine panel is scheduled^[11] to reevaluate the vaccine schedule at its Sept. 18 meeting. KFF Health News reported^[12] that the panel is expected to vote on whether to delay the vaccine until children are 4. 

Here’s what you should know about hepatitis B and what is behind the CDC’s longstanding “at birth” hepatitis B vaccine recommendation.

What is hepatitis B? 

The hepatitis B virus attacks the liver. Some people become very sick^[13] upon initial infection. Others have only mild symptoms or none at all. Acute cases can resolve on their own^[14], but sometimes they develop into chronic infections. 

Long-lasting infections can be asymptomatic, and dangerous. They develop more slowly and symptoms may not show up until much later in life, sometimes decades after the first exposure. 

“It’s a stealth infection,” said Dr. William Schaffner, Vanderbilt University School of Medicine professor and infectious disease expert. “After you get over the acute infection, you can have this smoldering infection and be contagious to others and feel perfectly normal.”

Untreated, chronic hepatitis B infections^[15] can cause cirrhosis and death. It is also one of the leading causes^[16] of liver cancer. Patients can seek treatments to reduce the virus’ worst effects. But there is no cure. 

The CDC^[17] estimates about 640,000 adults have chronic hepatitis B, but because of its asymptomatic nature, about half of people with the virus do not know they are infected and contagious.

Who gets hepatitis B and how? 

Anyone can get it. 

Hepatitis B is transmitted through bodily fluids^[18] like blood, semen and vaginal fluids. It is usually transmitted^[19] through sexual activity, direct contact with blood, or from mother to child during delivery due to contact with bodily fluids.

Because hepatitis B is an especially tough virus^[20], it can live outside^[21] the body on surfaces for up to seven days. Even a small amount can be infectious.

That means that although you can get it through sexual contact or health care work, mundane contact can also result in transmission. Small amounts^[22] of dried blood on innocuous household items^[23] like nail clippers^[24], razors or toothbrushes could be enough.

Many hepatitis B patients are never sure how they contracted it.

“Those environmental routes of transmission of hepatitis B undoubtedly play a small but notable role,” Schaffner said. 

Because so many people are unaware they are infected, preventing transmission was much more difficult — until the vaccine. 

How do babies get hepatitis B?

The fact that so many infected people have no idea they have it makes it nearly impossible to guarantee a child will never come into contact with a hepatitis B-positive individual.

Babies can get infected from their mothers during childbirth. Testing for hepatitis B during pregnancy is recommended^[25], and patients who receive regular prenatal care are highly likely to be tested at some point. But not all expecting mothers receive regular medical care. In some cases, those at highest risk for contracting hepatitis B are also less likely to access prenatal care, Schaffner said.

The vaccine works well^[26] to prevent infection in babies born to mothers with hepatitis B. 

But even if a mom tests negative, the child’s risk of contracting hepatitis is not zero. The reasons are varied: The test produces some false negatives. Pregnant patients can contract hepatitis B after being tested. Children may become infected simply by being in contact with the world at large.

Offit said that prior^[27] to the vaccine being recommended for all infants, around half^[28] of children under 10 were infected from their mother during birth. The other half contracted it somewhere else. 

How does the vaccine work and has it been effective at reducing cases? 

The hepatitis B vaccine was first^[29] introduced in 1981; the version in use today was put in place in 1986. 

It uses proteins^[30] from the surface of the hepatitis B virus to provoke an immune response^[31] that gives the body a defense against future infection. It is not a live virus, and the vaccine can’t infect someone with hepatitis B. 

Doctors expect the vaccine may provide lifelong protection^[32], but they are still monitoring results of the 39-year-old vaccine.

Prior to the vaccine, around 200,000 to 300,000 people were infected with hepatitis B each year^[33], including approximately 20,000 children, older CDC reports show. 

Since hepatitis B vaccines began being universally administered to babies, overall cases are down to around 14,000 annually.^[34] The change is especially dramatic^[35] among young people. In 2022, the CDC reported 252 new chronic hepatitis B^[36] infections among people up to age 19, or 0.4 out of every 100,000 kids. 

Dr. James Campbell, a University of Maryland pediatric infectious disease doctor, said the low rate is directly related to the recommended hepatitis B vaccine schedule: “Because we’ve been vaccinating nearly the entire population since 1991 those people are now 30 something years old.” New infections are largely among older Americans. 

All the doctors we spoke with, the CDC^[37] and the American Academy of Pediatrics^[38] describe the vaccine as safe and effective. 

But why not delay the vaccine until a child is a little older?

When it comes to hepatitis B, that first year of life is critical.

Whereas the Department of Health and Human Services^[39] reports that 90% of infants who become infected go on to develop a chronic hepatitis B infection, that rate is 2% to 6% for adults. And with research showing that 25% of infected infants^[40] die prematurely^[41] from the disease^[42], public health officials have long held that early delivery is crucial. 

“Think about it,” Campbell said. “We used to have 18,000 or 20,000 kids a year being born with this, a quarter of them going on to have liver cancer. We now have almost none.”

Delaying administration by even a few months increases a baby’s risk should they come into contact with the virus, Offit said. And Schaffner said delaying a vaccine can easily lead to never getting it: An unvaccinated child can become an unprotected adolescent or young adult with sexual partners, “and boom, then they get infected,” he said.  

What are the hepatitis B vaccine’s safety risks?

The most common side effects are mild and short term including pain or soreness where the shot is given, headache, fatigue or fever, according to the CDC^[43]. Very rarely^[44], some people have a severe allergic reaction^[45] to the shot called anaphylaxis, which can be treated. 

The vaccine contains small amounts of aluminium^[46], an additive used to enhance the body’s immune response. Although large amounts of aluminum can be harmful^[47], the vaccine contains less aluminum than infants get from their natural surroundings. 

According to the Children’s Hospital of Philadelphia, babies get about 4.4mg of aluminum^[48] from vaccines in their first six months; they get around 7mg from breastmilk and around 38 mg from formula in the same time. 

I heard that the risk of a baby dying from hepatitis B is 1 in 7 million. Is that wrong?

Health and Human Services Secretary Robert F. Kennedy used that statistic during recent Senate testimony. “That means you need to give 7 million hepatitis B vaccines to prevent one death,” he said.

The vaccine is not administered to prevent babies from dying as babies. It aims to prevent them from developing the more harmful chronic hepatitis B, which can be fatal when they get older. It also prevents severe illness. 

Kennedy’s statistic for babies who will eventually die from hepatitis B is still missing a lot of context.  

It’s based on a 2020 research paper^[49] that tried to quantify how many people would have died of hepatitis B in 2014 had there never been mass vaccination. 

The study estimated that 1,740 children ages 10 or younger would have contracted a deadly case of hepatitis B in a single year, 2014. 

But to make his “1 in 7 million” calculation, Kennedy left out 99% of those deadly cases — any considered to be due to “elevated risk” of exposure, including among children born to infected mothers, children living with infected individuals, or those in communities with large numbers of infected people. 

Since many people do not know they are infected, it can be hard to know if you are at elevated risk or reside in a community with infected individuals. 

Vaccines given at birth “protect not only infants and children in their infancy and childhood, but throughout their lives,” Schaffner said. “It’s a larger series of issues that we’re trying to address. We’re trying to protect not only babies, but the transmission of the virus to the next generation.”