A federal vaccine advisory committee plans to review the childhood vaccination schedule and scrutinize vaccines that have been approved for decades, fueling concerns that the panel may consider changes to long-standing vaccine recommendations.

On Wednesday, the newly appointed Advisory Committee on Immunization Practices convened for the first time. Earlier this month, Health Secretary Robert F. Kennedy Jr. fired all 17 members of the panel and appointed eight of his own, many of whom have expressed skepticism about the value and safety of vaccines. (One member, Dr. Michael Ross, has since withdrawn from the committee, Sen. Bill Cassidy, R-La., said Wednesday during a Senate hearing.)

The independent panel of experts makes recommendations to the Centers for Disease Control and Prevention about who should get certain vaccines, which can in turn influence whether the vaccines are covered by insurance.

The new committee chair, Martin Kulldorff — a biostatistician who criticized pandemic-era lockdowns and said he was fired from Harvard for refusing to get a Covid vaccination — struck a combative tone as the meeting began.

“Some media outlets have been very harsh on the new members of this committee, issuing false accusations and making concerted efforts to put scientists in either a pro- or anti-vaccine box,” Kulldorff said. “Such labels undermine critical scientific inquiry, and it further feeds the flames of vaccine hesitancy.”

Kulldorff also said that he opposed federal health agencies’ decision to temporarily pause the rollout of Johnson & Johnson’s Covid vaccine due to reports of rare blood clots in young women.

“There was a shortage of vaccines and people were dying, so I think that pause of the J&J vaccine was inappropriate,” Kulldorff said. “So in that case, I was, I guess, the most pro-vaccine person among vaccine scientists in this country. So it’s kind of a little bit ridiculous that then the media says that I am anti-vaccine.”

He also announced the creation of two new work groups, subdivisions of the independent panel that review vaccine data and develop recommendation options to present at ACIP meetings.

One will look at the cumulative effect of recommended childhood vaccines, including potential interaction effects between the shots. Another will re-evaluate vaccines that haven’t been reviewed in more than seven years, Kulldorff said, including hepatitis B vaccines and a combination vaccine that protects against measles, mumps, rubella and varicella.

“This was supposed to be a regular practice of the ACIP, but it has not been done in a thorough and systematic way,” he said at the meeting.

Kennedy has frequently criticized the childhood vaccination schedule, including the fact that children are vaccinated against far more diseases compared with decades ago.

“When I was a kid I got three vaccines,” Kennedy said Tuesday during a congressional hearing. “Today they get 69 to 92 jabs of vaccines between conception and when they are 18 years old.”

Health Secretary Robert F. Kennedy Jr. in the Oval Office on April 18. Andrew Harnik / Getty Images

However, many vaccine experts argue that today’s shots contain fewer antigens — the key components of vaccines that train the immune system to recognize the germ — compared with generations ago, and are therefore less taxing on the immune system.

In announcing the new ACIP work groups on Wednesday, Kulldorff questioned some of the committee’s past recommendations, including that hepatitis B vaccines should be given to newborns and that it’s acceptable for 1-year-olds to receive a shot that combines the measles-mumps-rubella vaccine with the chickenpox, or varicella, vaccine.

“Unless the mother is hepatitis B positive, an argument could be made to delay the vaccine for this infection, which is primarily spread by sexual activity and intravenous drug use,” he said.

The combination measles, mumps, rubella and varicella (MMRV) vaccine was approved in 2005 and the CDC initially recommended it be given to children at 12-15 months and again at ages 4 to 6. However, the CDC changed its guidance in 2009 after the first dose was linked to an increased risk of febrile seizures — convulsions caused by a spike in temperature — for every 2,300 to 2,600 vaccinated children.

Now, the CDC recommends that young children are vaccinated with the MMR vaccine and the separate varicella vaccine for their first dose, and the combination shot be used for the second dose. However, the overall risk of febrile seizures is very low for both options, according to the agency.

Kulldorff questioned a past ACIP recommendation that, for their first dose, children can get either the combination shot or separate varicella and MMR vaccines.

He also said the working group “may also look at new research concerning the optimal timing of the MMR vaccine to resolve religious objections that some parents have concerning the MMR vaccine being used here in the United States. They could also look at other MMR vaccines, such as the one used in Japan.”

Over the next two days, the panel is slated to discuss updated data on anthrax, chikungunya, Covid and MMRV vaccines and vote on RSV and influenza vaccines.

Recent Covid work group discussions presented Wednesday determined that updated Covid vaccines are suitable for pregnant women, babies ages 6 to 23 months, and children and adults ages 2 to 64 who are at high risk of exposure to Covid. Immunocompromised people older than 6 months and older adults ages 65 and up should get two doses of the updated shot, according to the work group discussions.

The group also determined that healthy children and adults could talk with their doctors about getting an updated Covid vaccine. In May, Kennedy announced that the CDC was no longer recommending the vaccine for this group or pregnant women.

In another presentation for Wednesday afternoon, a work group determined that the CDC should recommend clesrovimab, an antibody injection that can prevent RSV, for all infants less than 8 months old born during or entering their first RSV season. The group determined that the drug was effective at preventing severe RSV in young infants and had a favorable safety profile. However, it also noted that too few infants were included in the clinical trial to capture rare adverse events.

The drug, from Merck, was approved by the Food and Drug Administration earlier this month. A similar drug, nirsevimab, is already approved and recommended for these infants.

On Thursday, Lyn Redwood, an anti-vaccine activist, is set to give a presentation on thimerosal, a mercury-based preservative removed from all childhood vaccines — except for certain flu shots — in 2001. Redwood is the president emerita of Children’s Health Defense, the anti-vaccine nonprofit group founded by Kennedy. She also co-founded SafeMinds, a group that funded research it hoped would show that thimerosal in vaccines was linked to autism. There is no evidence of such a link.

The CDC’s vaccine advisory committee is set to vote Thursday on whether thimerosal should remain in certain flu vaccines.

Redwood’s presentation claims that “removing a known neurotoxin from being injected into our most vulnerable populations is a good place to start with Making America Healthy Again.” But there’s no evidence that the low doses of thimerosal in flu vaccines are harmful, beyond some redness or swelling at the injection site. The preservative consists of ethylmercury, which is far less likely to accumulate in the body than mercury found in the environment. And the bulk of scientific evidence has shown that low doses in vaccines don’t harm the nervous system.