After a contentious discussion that at times referenced discredited theories, low-quality data and desperate pleas from physicians and patients to rely upon sound science, a key CDC committee opted Friday to weaken its existing recommendations on COVID-19 shots, while punting other vaccine decisions to a later date.

The Advisory Committee on Immunization Practices voted unanimously to pull back its current unequivocal recommendation that all adults get vaccinated against COVID-19 in favor of a process of “shared clinical decision making,” in which patients are encouraged to speak to a doctor, nurse or pharmacist first.

The group came extremely close to recommending that the COVID-19 vaccine be available by prescription only, with a 6-6 vote broken by chair Martin Kulldorff’s “no” vote. The group also postponed a vote on hepatitis B vaccination indefinitely, with some members arguing that a proposal to delay the first dose did not go far enough.

The two-day meeting’s chaotic atmosphere left even many close observers confused about what decisions the group actually made.

“What we’re seeing is what happens when individuals who don’t have a basic understanding about how vaccines are delivered are making these crucial policy decisions for the American public. They don’t know what they’re doing,” Dr. Sean O’Leary, chair of American Academy of Pediatrics’ Committee on Infectious Diseases, said Friday during a news conference over Zoom. “What we are getting from ACIP is confusion.”

On Thursday, the committee voted that children under the age of four receive the measles, mumps and rubella (MMR) vaccine and the varicella, or chickenpox, vaccine in two separate shots given at the same time, instead of a single dose.

It was a relatively minor change. Many pediatricians already do this in order to reduce the risk of febrile seizures.

But the meeting’s tone and the decisions the committee appeared poised to make profoundly worried many physicians and public health officials.

“The damage isn’t just in today’s specific votes, it’s in legitimizing this framework where these laboratory-based studies and theories based on misrepresented findings are given equal standing with robust population-level safety data,” Dr. Jake Scott, an infectious disease specialist at Stanford University School of Medicine, said Friday. “Now every anti-vax group knows that they can package their claims and scientific-looking slides and cite some weird paper out of context, and then potentially get their concerns mandated into official medical documents.”

The COVID-19 discussion was led by Retsef Levi, a professor of operations management at MIT Sloan and the lone member of the committee with no biomedical or clinical degree.

He began the discussion by making clear that the committee would take into account anecdotal evidence and unpublished reports in its decision making, together with rigorously researched data.

“We need to leverage all the relevant published and unpublished scientific, clinical and public health data, information and knowledge, including experiences from the field. We are going to focus on personalized risk benefit analysis, and we’re going to very much stay away from the narratives or the statements about ‘safe and effective,’” said Levi, who has stated that mRNA vaccines are deadly and should be pulled from the market. “We don’t believe that these are appropriate or scientific language to talk about the issues related to vaccination.”

At one point, a microphone caught someone in the meeting muttering “idiot” as Levi was talking. It was not clear who the speaker was.

The group voted unanimously to postpone any changes to hepatitis B vaccination. Vaccine skeptics appointed to the committee said that a proposal to delay the first dose by a month didn’t go far enough.

ACIP member Vicky Pebsworth, a nurse who serves as research director for the National Vaccine Information Center, an organization long criticized for promoting inaccurate information, criticized the CDC for glossing over side effects of hepatitis B vaccine such as fever, sleepiness and fussiness.

“These are not trivial reactions,” Pebsworth said. “I personally think we should be erring on the side of caution and adopt a more prudent vaccination policy.”

Hepatitis B has been nearly eliminated since the vaccine was introduced in 1991.

Up to 85% of babies born to infected mothers become infected themselves, and the risk of long-term effects from the disease is higher the earlier the infection is acquired.

Infants infected in the first year of life have a 90% chance of developing chronic hepatitis B and 25% of those who do will die from complications such as liver cancer and cirrhosis, according to the American Academy of Pediatrics.

Side effects from the vaccine are extremely rare, CDC scientists told the committee Thursday, and those that do occur tend to be mild.

Several committee members indicated they were unconvinced.

“There are gaps in what we know and understand about the effects of hepatitis B [vaccine], particularly on very young infants, and the conclusion that we know that it is safe is perhaps premature,” Pebsworth said.

At one point, she asked whether the irritability and fussing some babies showed at the time of the shot could be early symptoms of neurological problems stemming from the vaccine that hadn’t been studied.

At this, committee member Dr. Joseph Hibbeln pushed back.

“We have to vote on where there’s data of concrete harm or concrete benefit,” said Hibbeln, a psychiatrist who previously served as a section chief at the National Institutes of Health. “We’re going beyond data, and we’re turning into a discussion of speculation and possible clinical outcomes for which we have no data.”

The American Academy of Pediatrics said in a news conference Thursday that it would continue to recommend that infants receive their first hepatitis B shot at birth.

America’s Health Insurance Plans, an association that includes major U.S. insurers such as Aetna, Humana, Kaiser Permanente, Cigna and several Blue Cross and Blue Shield groups, announced this week that its members would continue to cover all vaccines recommended by the CDC as of Sept. 1 through the end of 2026.

For most of its 61-year history, ACIP meetings have been dry, technical affairs in which committees of experienced physicians, public health officials and research scientists get deep into the weeds of vaccine and disease data.

The committee’s role in vaccine insurance coverage and availability in the U.S. is paramount. Insurers are only required to cover vaccines the CDC endorses, though they can choose to cover others as well. The committee’s recommendation has typically set the vaccine schedule followed by schools and physicians. It also determines what vaccines are covered by the CDC’s Vaccines for Children Program, which pays to immunize nearly half the nation’s children.

Previously, the committee collaborated year-round with expert working groups like the American Medical Assn., the American Academy of Pediatrics and the Infectious Diseases Society of America to craft its recommendations and guidelines. Members also served staggered terms, so that new people coming on always joined colleagues with previous experience, and often went through more than a year of vetting.

But Kennedy fired the entire 17-member committee in June, and then informed medical groups they were no longer invited to review scientific evidence and advise the committee in advance of the meeting.

With the exception of Dr. Cody Meissner, who served on ACIP under presidents George W. Bush and Barack Obama, all of the members are new.

The lack of experience showed.

The group started the day by redoing a vote they’d hurriedly cast the previous afternoon on whether public funding would continue to cover the combined MMRV shot, as several members confessed to not fully understanding the text of the measure they’d voted on. In the new vote, they determined that it would not.

In August, Kennedy fired CDC Director Susan Monarez, who was appointed to the position by President Trump. On Wednesday, Monarez told a Senate committee that Kennedy fired her in part because she refused to sign off in advance on changes he planned to make to the vaccine schedule this month, without seeing scientific evidence for them.

The ACIP’s recommendations become official only after the CDC director approves them. With Monarez out, that responsibility now goes to Health and Human Services Deputy Secretary Jim O’Neill, who is serving as the CDC’s acting director.

“This committee has focused on poorly done research that supports their preconceived anti-vaccine notions, rather than trying to truly weigh risks and benefits to get to the best decisions for American kids,” said Dr. Adam Ratner, a New York City pediatric infectious disease specialist. “This ACIP meeting demonstrates a sad deterioration of our public health systems, and real families and children will suffer as a result.”