Health and Human Services Secretary Robert F. Kennedy Jr. and the members of his newly appointed vaccine panel are casting doubt on the hepatitis B vaccine and the established practice of vaccinating newborns.

Last week, during the first meeting of the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) since Kennedy removed all the previous sitting members and appointed seven new members, the chair questioned whether it was "wise" to administer shots "to every newborn before leaving the hospital."

Martin Kulldorff, a former Harvard Medical School professor, said a new work group would discuss the practice.

Additionally, Kennedy claimed, without evidence, earlier this week during an interview with Tucker Carlson, that the CDC conducted a study that found the hepatitis B vaccine increases the risk of autism, and that researchers hid the results of the study from the public.

The HHS did not immediately respond to ABC News' request for the study that Kennedy referenced in his interview.

An infectious disease expert told ABC News that there is no evidence to suggest the hepatitis B vaccine is unsafe and that vaccinating babies at birth has been key to virtually eliminating the virus among children. 

Hepatitis B is a liver infection caused by the hepatitis B virus, according to the CDC. The virus is transmitted from a person coming into contact with the blood, semen or other bodily fluid of someone who is infected.

Newborns might be infected through the process of birth or from casual contact, because the virus can survive in the environment for about a week, Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, told ABC News.

Up to half of all older children, adolescents and adults have symptoms of acute hepatitis B. Most children younger than age 5, however, have no symptoms, the CDC said.

"Hepatitis B … causes inflammation in the liver …and that inflammation leads to the liver not working well at all," Chin-Hong said. "So that's cirrhosis and liver failure and, ultimately, also liver cancer. The longer you have hepatitis B, the higher the risk of cirrhosis or liver failure and liver cancer."

Acute hepatitis B infection, which is a short-term illness, can lead to a lifelong infection known as chronic hepatitis B, according to the CDC

Chin-Hong said that means if somebody is born with hepatitis B or infected as a child, they have a high chance of liver failure or liver cancer as an adult.

Chin-Hong said the best way for someone to prevent hepatitis B and to protect themselves is by getting vaccinated.

The vaccine was first developed in the early 1980s. Depending on the vaccine brand, the hepatitis B vaccine is either a series of two or three shots, according to the CDC.

The childhood immunization schedule recommends babies be vaccinated at birth with a second dose between one and two months old and a potential third dose from 6 months to 15 months old.

"The more shots you get, the higher the chance the vaccine will take," Chin-Hong said. "If you get three shots, it's above 97% efficacy."

In 1991, when the ACIP recommended universal vaccination for hepatitis B among infants to decrease transmission, there were 18,000 cases of hepatitis B in those under 10 years old in the U.S., according to the CDC.

Since then, cases have dramatically decreased. CDC data shows that in 2022, the rate of cases among those ages 19 was less than 0.1 per 100,000.

"It's very, very rare," Chin-Hong said. "So, we've had a big success, and the United States is a mirror for the rest of the world … 97% of countries now have a recommendation for hepatitis B vaccination in infants. It's really changed the face of not only infection and liver failure, but also liver cancer."

During the ACIP meeting last week, Kulldorff implied that children receive too many vaccines nowadays compared to decades ago.

"The number of vaccines that our children and adolescents receive today exceeds what children in most other developed nations receive and what most of us in this room received when we were children," Kulldorff said.

Chin-Hong said that by adding vaccines to the immunization schedule, children have more protection against diseases compared to 10 or even 20 years ago, and the makeup of vaccines is also different.

"The way that we're delivering the vaccines is very different," he said. "They're through smaller bits of the virus instead of the whole virus itself or bacteria. So, it means that infants are exposed to actually fewer antigens. or parts of the virus or bacteria, with better vaccines."

The ACIP announcing that well-studied vaccines, like the hepatitis B vaccine, are going to be reanalyzed could make people think the initial approval process was unsafe, according to Chin-Hong.

As for Kennedy's claim, the HHS secretary has been a long-time vaccine skeptic who refused to say during his confirmation hearings earlier this year that vaccines don't cause autism despite many high-quality studies finding no such link.

"There's no evidence that the hepatitis B vaccine leads to autism or is a risk factor for autism, and that is unquestionable," Chin-Hong said.

ABC News' Youri Benadjaoud contributed to this report.