A new, highly transmissible COVID subvariant has been detected in California — heightening the risk of a potential summer wave as recent moves by the Trump administration threaten to make vaccines harder to get, and more expensive, for many Americans, some health experts warn.

Health and Human Services Secretary Robert F. Kennedy Jr. announced this week that he was rescinding the federal government’s recommendation that pregnant women and healthy children get immunized against COVID, effective immediately.

Dr. Marty Makary, commissioner of the U.S. Food and Drug Administration, also said the agency will no longer routinely approve annually formulated COVID-19 vaccinations for healthy people under age 65.

“We simply don’t know whether a healthy 52-year-old woman with a normal BMI who has had COVID-19 three times and has received six previous doses of a COVID-19 vaccine will benefit from the seventh dose,” Makary, along with another FDA official, Dr. Vinay Prasad, wrote in the New England Journal of Medicine this month. “This policy will compel much-needed evidence generation.”

However, some experts say mandating more extensive testing could delay vaccine access for many, as those efforts may not even be complete until after the end of the upcoming winter flu-and-COVID season.

“Pregnant women, infants and young children are at higher risk of hospitalization from COVID, and the safety of the COVID vaccine has been widely demonstrated,” Dr. Sean O’Leary, chair of the American Academy of Pediatrics’ Committee on Infectious Diseases, said in a statement.

The U.S. Centers for Disease Control and Prevention has said that, in general, getting an updated vaccine provides children and adults additional protection from COVID-related emergency room and urgent care visits.

The recent federal changes, according to some experts, could also prompt private insurance companies and government insurers to stop paying for COVID shots for wide segments of the population, including babies and children.

Absent a recommendation by federal officials, Americans could end up paying the entire cost of a vaccine, experts say. The out-of-pocket cost for a COVID vaccine at CVS, for instance, is $198.99.

Although the emergency phase of the pandemic has long since passed, authorities note COVID remains a public health concern. A relatively new subvariant has been spreading in Europe and Asia, “particularly Hong Kong, Taiwan, other countries, Japan, etc.,” said Dr. Peter Chin-Hong, a UC San Francisco infectious diseases expert.

That subvariant, NB.1.8.1, was first documented in January and has since been detected in California, including in Los Angeles County and the San Francisco Bay Area. The World Health Organization designated it a “Variant Under Monitoring” last week.

NB.1.8.1 has grown exponentially worldwide in recent weeks. The Omicron subvariant represented 10.7% of genetically analyzed viral samples worldwide for the week ending April 27, WHO data show. That was up sharply from the week ending April 6, when the subvariant accounted for 2.5% of samples worldwide.

“While still low numbers, this is a significant rise,” the WHO said, adding that there was a “concurrent increase in cases and hospitalizations in some countries where NB.1.8.1 is widespread.”

NB.1.8.1 isn’t yet prevalent enough in the United States to be publicly tracked by the CDC. Another strain, LP.8.1, accounted for an estimated 73% of coronavirus specimens nationally for the two-week period ending Saturday.

Data suggest NB.1.8.1 does not cause more severe illness, “but it is more transmissible, at least from what we’re seeing around the world and also from lab experiments,” said Dr. Yvonne Maldonado, an infectious-disease expert at Stanford University.

In Taiwan, a top health official told reporters that an NB.1.8.1-fueled outbreak was “continuing to rise rapidly, with a sustained increase in severe and fatal cases,” the Central News Agency reported, prompting a shortage of COVID testing kits. Health officials said a factor in Taiwan’s surge was the lack of a major COVID wave over the winter, and forecast that the island’s current spike may not peak for another four to six weeks.

NB.1.8.1 has seen increased prevalence in each of the three WHO regions that still consistently share genetic analysis of COVID samples — the Western Pacific (which includes East Asia, parts of Southeast Asia, and Australia); Europe; and the Americas.

The rate at which COVID tests are coming back positive in Los Angeles County has slightly increased over the past few weeks, although the overall positive rate remains low, at 3.5%, according to the county Department of Public Health. Coronavirus levels detected in the county’s wastewater have increased by 6% in the last three weeks, but also remain relatively low and are about one-eighth of the peak in the summer of last year.

Although California experienced a mild winter season — a first of the COVID era — that followed a powerful summer spike that was the strongest in years.

Many experts and officials have touted available COVID vaccines as effective both in warding off infection and in lessening the severity of symptoms. However, the need for otherwise healthy individuals to roll up their sleeves has been a matter of debate.

In a video message Tuesday on X, Kennedy — a noted vaccine skeptic — said that he “couldn’t be more pleased to announce that, as of today, the COVID vaccine for healthy children and healthy pregnant women has been removed from the CDC recommended immunization schedule.”

Experts said they could not recall a time when a political appointee circumvented a well-established process of making vaccine recommendations, which typically involves panels of scientists advising the FDA and CDC.

“It’s kind of chilling,” Chin-Hong said. “It’s out of step with the system we’ve learned to trust and follow.”

In a statement to The Times, the L.A. County Department of Public Health urged Kennedy to listen to experts in the field — including from the CDC’s Advisory Committee on Immunization Practices, which is scheduled to meet next month — “before decreasing access to any vaccine.”

As of Thursday, the CDC still had the long-standing vaccine recommendations on its website: Everyone ages 6 months and older should get the most recent COVID-19 vaccine, officially known as the 2024-25 version, which was introduced in September. The CDC also recommends seniors ages 65 and up get a second vaccine dose six months after their first.

In a statement, the California Department of Public Health said that it supports the current expansive recommendation for COVID vaccines, and that it “will continue to follow the federal conversation through this dynamic situation.”

“Staying up to date with COVID-19 vaccination can reduce the risk of disease, especially more severe cases that result in hospitalization or death,” the department added.

The Washington Post reported Wednesday that the CDC did not know of Kennedy’s directive until he posted it, and officials have been “scrambling to find out what it meant.”

Experts who spoke with The Times warned the practical effect of the edict — if it becomes official — could be far more costly vaccines for affected groups.

“If vaccines are not recommended by the CDC, insurance companies would NOT be required to cover the cost,” the L.A. County Department of Public Health said in a statement.

As a result, the vaccines may be less accessible to healthier people who still want them — perhaps because they live or work with elderly or other higher-risk people, they’ve had severe COVID illness before, or they want to protect themselves against the latest subvariant, the agency said.

If the FDA withholds a license for an updated COVID vaccination for younger, healthier adults, this group “would not be able to receive it unless their provider chooses to give it ‘off label,’” the county said.

When asked whether healthy pregnant women and healthy children can still get vaccinated at its pharmacies, Walgreens said its teams operate “in full compliance with applicable laws.” CVS said its locations “follow federal guidance regarding vaccine administration and are monitoring any changes that the government may make regarding vaccine eligibility.”

Kaiser Permanente Southern California said it was aware of potential changes, but noted no new formal guidance has yet been issued. As a result, Kaiser is continuing to follow existing guidance, which recommends the shots for everyone.

The L.A. County Department of Public Health said that as of Wednesday, “pregnant women and healthy children can get vaccinated for COVID-19,” according to existing recommendations from an advisory panel and the CDC.

Chin-Hong noted there were 150 pediatric deaths in the U.S. from COVID-19 in a recent one-year period. That’s in the same ballpark as the 231 pediatric flu deaths recorded this season, and federal health officials recommend everyone ages 6 months and older get an annual flu shot.

“Most people would agree that kids should be targeted for flu vaccines. It seems kind of weird to have COVID as an outlier in that respect,” Chin-Hong said.

In the video published this week, Makary said that “most countries in the world have stopped recommending the vaccine for children.”

Maldonado, however, said the U.S. doesn’t use other nations’ standards to dictate vaccine recommendations. The U.S., for instance, recommends other types of vaccines that have a lower prevalence than COVID that people want to get, Maldonado said, such as the meningococcal vaccine for children to guard against a serious bacterial disease that can infect the brain and spinal cord and cause death within hours.

The effect of a recommendation also varies by country. Canada, for instance, recommends updated COVID vaccines for seniors and other people who meet certain criteria, such as if they’re pregnant or are a healthcare worker. But the country’s universal healthcare system still allows everyone ages 6 months and older to get an updated COVID vaccine.

Although it’s true that children overall are at lower risk of developing severe COVID illness, those under 6 months of age “have the same risk of complications as the 65-year-old-plus population in this country,” said Stanford’s Maldonado, who also serves on the CDC’s Advisory Committee on Immunization Practices.

Among children eligible for vaccination, COVID-associated hospitalization rates are highest for those ages 6 months to 4 years, according to the CDC.

“So are children going to be the highest risk group? No, they’re not. But would you want to protect your child from a disease that could potentially put them in the hospital and get them on a ventilator? Yes, I would say that I would want to make that choice for myself. And why not allow the parent to make that choice?” Maldonado said.

The CDC says COVID vaccination during pregnancy builds antibodies that can help protect the baby; studies have also shown that vaccinated moms who breastfeed have protective antibodies in their milk, which could help protect their babies.

There have been an estimated 260,000 to 430,000 hospitalizations attributed to COVID since October, causing “an enormous burden on the healthcare system,” Dr. Fiona Havers, a medical epidemiologist with the CDC, said at a recent public meeting. There have also been an estimated 30,000 to 50,000 COVID-19 deaths over the same time period.

“It is a major cause of morbidity and mortality, particularly in older adults, but it does affect other people, particularly those with underlying conditions, in younger age groups.”

COVID is also a major cause of pediatric hospitalizations, even among otherwise healthy children, she said.

“If there’s a summer wave this year, we’ll be seeing it in children being hospitalized with COVID as well,” she said.