For most American infants, the hepatitis B shot comes just before their first bath, in the blur of pokes, prods and pictures that attend a 21st century hospital delivery.

But as of this week, thousands of newborns across the U.S. will no longer receive the initial inoculation for hepatitis B — the first in a litany of childhood vaccinations and the top defense against one of the world’s deadliest cancers.

On Dec. 5, the Centers for Disease Control and Prevention’s powerful vaccine advisory panel voted to nix the decades-old birth-dose recommendation.

The change was pushed by Health and Human Services Secretary Robert F. Kennedy Jr. and his “Make America Healthy Again” movement, which has long sought to rewrite the CDC’s childhood vaccine schedule and unwind state immunization requirements for kindergarten.

California officials have vowed to keep the state’s current guidelines in place, but the federal changes could threaten vaccine coverage by some insurers and public benefits programs, along with broader reverberations.

“It’s a gateway,” said Jessica Malaty Rivera, an infectious disease epidemiologist in Los Angeles. “It’s not just hepatitis B — it’s chipping away at the entire schedule.”

Democratic-led states and blue-chip insurance companies have scrambled to shore up access. California joined Hawaii, Oregon and Washington in forming the West Coast Health Alliance to maintain uniform public policy on vaccines in the face of official “mis- and dis-information.”

“Universal hepatitis B vaccinations at birth save lives, and walking away from this science is reckless,” California Gov. Gavin Newsom said in a statement. “The Trump administration’s ideological politics continue to drive increasingly high costs — for parents, for newborns, and for our entire public-health system.”

The issue is also already tied up in court.

On Tuesday, the Supreme Court sent a lawsuit over New York’s vaccine rules back to the 2nd U.S. Circuit Court of Appeals for review, signaling skepticism about the stringent shots-for-school requirements pioneered in California. On Friday, public health officials in Florida appeared poised to ax their schools’ hepatitis B immunization requirement, along with shots for chickenpox, a dozen strains of bacterial pneumonia and the longtime leading cause of deadly meningitis.

Boosters of the hep B change said it replaces impersonal prescriptions with “shared clinical decision-making” about whether and how to vaccinate, while preserving the more stringent recommendation for children of infected mothers and those whose status is unknown.

Critics say families were always free to decline the vaccine, as about 20% did nationwide in 2020, according to data published by the CDC. It’s the only shot on the schedule that children on Medicaid receive at the same rate as those with private insurance.

Rather than improve informed consent, critics say the CDC committee’s decision and the splashy public fight leading up to it have depressed vaccination rates, even among children of infected mothers.

“Hepatitis B is the most vulnerable vaccine in the schedule,” said Dr. Chari Cohen, president of the Hepatitis B Foundation. “The message we’re hearing from pediatricians and gynecologists is parents are making it clear that they don’t want their baby to get the birth dose, they don’t want their baby to get the vaccine.”

Much of that vulnerability has to do with timing: The first dose is given within hours of birth, while symptoms of the disease might not show up for decades.

“The whole Day One thing really messes with people,” Rivera said. “They think, ‘This is my perfect fresh baby and I don’t want to put anything inside of them.’ ”

U.S. surgeon general nominee Casey Means called the universal birth dose recommendation “absolute insanity,” saying in a post on X last year that it should “make every American pause and question the healthcare system’s mandates.”

“The disease is transmitted through needles and sex exclusively,” she said. “There is no benefit to the baby or the wider population for a child to get this vaccine who is not at risk for sexual or IV transmission. There is only risk.”

In fact, at least half of transmission occurs from mother to child, typically at birth. A smaller percentage of babies get the disease by sharing food, nail clippers or other common household items with their fathers, grandparents or day-care teachers. Because infections are often asymptomatic, most don’t know they have the virus, and at least 15% of pregnant women in the U.S. aren’t tested for the disease, experts said.

Infants who contract hepatitis B are overwhelmingly likely to develop chronic hepatitis, leading to liver cancer or cirrhosis in midlife. The vaccine, by contrast, is far less likely than those for flu or chickenpox to cause even minor reactions, such as fever.

“We’ve given 50 billion doses of the hepatitis B vaccine and we’ve not seen signals that make us concerned,” said Dr. Su Wang, medical director of Viral Hepatitis Programs and the Center for Asian Health at the Cooperman Barnabas Medical Center in New Jersey, who lives with the disease.

Still, “sex and drugs” remains a popular talking point, not only with Kennedy allies in Washington and Atlanta, but among many prominent Los Angeles pediatricians.

“It sets up on Day One this mentality of, ‘I don’t necessarily agree with this, so what else do I not agree with?’” said Dr. Joel Warsh, a Studio City pediatrician and MAHA luminary, whose recent book “Between a Shot and a Hard Place” is aimed at vaccine-hesitant families.

Hepatitis B also disproportionately affects immigrant communities, further stigmatizing an illness that first entered the mainstream consciousness as an early proxy for HIV infection in the 1980s, before it was fully understood.

At the committee meeting last week, member Dr. Evelyn Griffin called illegal immigration the “elephant in the room” in the birth dose debate.

The move comes as post-pandemic wellness culture has supercharged vaccine hesitancy, expanding objections from a long-debunked link between the measles-mumps-rubella vaccine and autism to a more generalized, equally false belief that “healthy” children who eat whole foods and play outside are unlikely to get sick from vaccine-preventable diseases and, if they do, can be treated with “natural” remedies such as beef tallow and cod liver oil.

“It’s about your quality of life, it’s about what you put in your body, it’s about your wellness journey — we have debunked this before,” Rivera said. “This is eugenics.”

Across Southern California, pediatricians, preschool teachers and public health experts say they’ve seen a surge in families seeking to prune certain shots from the schedule and many delay others based on “individualized risk.” The trend has spawned a cottage industry of e-books, Zoom workshops by “vaccine friendly” doctors offering alternative schedules, bespoke inoculations and post-vaccine detox regimens.

CDC data show state exemptions for kindergarten vaccines have surged since the height of the COVID-19 pandemic, with about 5% of schoolchildren in Georgia, Florida and Ohio, more than 6% in Pennsylvania and nearly 7% in Michigan waved out of the requirement last year.

In Alaska and Arizona, those numbers topped 9%. In Idaho, 1 in 6 kindergartners are exempt.

California is one of four states — alongside New York, Connecticut and Maine — with no religious or personal-belief exemptions for school vaccines.

It is also among at least 20 states that have committed to keep the hepatitis B birth dose for babies on public insurance, which covers about half of American children. It is not clear whether the revised recommendation will affect government coverage of the vaccine in other states.

Experts warn that the success of the birth-dose reversal over near-universal objection from the medical establishment puts the entire pediatric vaccination schedule up for grabs, and threatens the school-based rules that enforce it.

Ongoing measles outbreaks in Texas and elsewhere that have killed three and sickened close to 2,000 show the risks of rolling back requirements, experts said.

Hepatitis is not nearly as contagious as measles, which can linger in the air for about two hours. But it’s still fairly easy to pick up, and devastating to those who contract it, experts said.

“These decisions happening today are going to have terrible residual effects later,” said Rivera, the L.A. epidemiologist. “I can’t imagine being a new mom having to navigate this.”