After more than five decades of trying, the drug industry is on the verge of providing effective immunizations against the respiratory syncytial virus, which has put an estimated 90,000 U.S. infants and small children in the hospital since the start of October.

But only one of the shots is designed to be given to babies, and a glitch in congressional language may make it difficult to allow children from low-income families to get it as readily as the well-insured.

Since 1994, routine vaccination has been a childhood entitlement under the Vaccines for Children program, through which the federal government buys millions of vaccines and provides them free through pediatricians and clinics to children who are uninsured, underinsured, or on Medicaid — more than half of all American kids.

The 1993 law creating the program didn’t specifically include antibody shots, which were used only as rare emergency therapy at the time the bill was written.

But the first medication of its kind likely to be available to babies, called nirsevimab (it was approved in Europe in December, and FDA approval is expected this summer), is not a vaccine but rather a monoclonal antibody that neutralizes RSV in the bloodstream.

The Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices is certain to recommend giving the antibody to infants, said Dr. Kelly Moore, president of the advocacy group The CDC is currently assessing whether nirsevimab would be eligible for the Vaccines for Children program, agency spokesperson Kristen Nordlund told KHN.

Failing to do so would “consign thousands upon thousands of infants to hospitalization and serious illness for semantic reasons despite existence of an immunization that functionally performs just like a seasonal vaccine,” Moore said.

Officials from Sanofi, which is producing the nirsevimab injection along with AstraZeneca, declined to state a price but said the range would be similar to that of a pediatric vaccine course. The CDC pays about $650 for the most expensive routine vaccine, the four shots against pneumococcal infection. In other words, FDA approval would make nirsevimab a blockbuster drug worth billions annually if it’s given to a large share of the 3.7 million or so children born in the U.S. each year.

Pfizer and GSK are making traditional vaccines against RSV and expect FDA approval later this year. Pfizer’s shot initially would be given to pregnant women — to shield their babies from the disease — while GSK’s would be given to the elderly.

Vaccines designed for infants are in the pipeline, but some experts are still nervous about them. A 1966 RSV vaccine trial failed spectacularly, killing two toddlers, and immunologists aren’t totally in agreement over the cause, said Dr. Barney Graham, the retired National Institutes of Health scientist whose studies of the episode contributed to successful covid-19 and RSV vaccines.

After two years of COVID lockdowns and masking slowed its transmission, RSV exploded across the United States this year, swamping pediatric intensive care units.

Sanofi and AstraZeneca hope to have nirsevimab approved by the FDA, recommended by the CDC, and deployed nationwide by fall to prevent future RSV epidemics.

Their product is designed to be provided before a baby’s first winter RSV season. In clinical trials, the antibodies provided up to five months of protection. Most children wouldn’t need a second dose because the virus is not a mortal danger to healthy kids over a year old, said Jon Heinrichs, a senior member of Sanofi’s vaccines division.

If the antibody treatment is not accepted for the Vaccines for Children program, that will limit access to the shot for the uninsured and those on Medicaid, the majority of whom represent racial or ethnic minorities, Moore said. The drugmakers would have to negotiate with each state’s Medicaid program to get it on their formularies.

Excluding the shot from Vaccines for Children “would only worsen existing health disparities,” said Dr. Sean O’Leary, a professor of pediatrics at the University of Colorado and chair of the infectious diseases committee of the American Academy of Pediatrics.

RSV affects babies of all social classes but tends to hit poor, crowded households hardest, said Graham. “Family history of asthma or allergy makes it worse,” he said, and premature babies are also at higher risk.

While 2% to 3% of U.S. infants are hospitalized with RSV each year, only a few hundred don’t survive. But as many as 10,000 people 65 and older perish because of an infection every year, and a little-discussed legal change will make RSV and other vaccines more available to this group.

A section of the 2022 Inflation Reduction Act that went into effect Jan. 1 ends out-of-pocket payments for all vaccines by Medicare patients — including RSV vaccines, if they are licensed for this group.

Before, “if you hadn’t met your deductible, it could be very expensive,” said Dr. Leonard Friedland, vice president for scientific affairs and public health in GSK’s vaccines division, which also makes shingles and combination tetanus-diphtheria-whooping cough boosters covered by the new law. “It’s a tremendously important advance.”

Of course, high levels of vaccine hesitancy are likely to blunt uptake of the shots regardless of who pays, said Jennifer Reich, a University of Colorado sociologist who studies vaccination attitudes.

New types of shots, like the Sanofi-AstraZeneca antibodies, often alarm parents, and Pfizer’s shot for pregnant women is likely to push fear buttons as well, she said.

Public health officials “don’t seem very savvy about how to get ahead” of claims that vaccines undermine fertility or otherwise harm people, said Reich.

On the other hand, this winter’s RSV epidemic will be persuasive to many parents, said Heidi Larson, leader of the Vaccine Confidence Project and a professor of anthropology at the London School of Hygiene and Tropical Medicine.

“It’s a scary thing to have your kid hospitalized with RSV,” she said.

While unfortunate, “the high number of children who died or were admitted to the ICU in the past season with RSV — in some ways that’s helpful,” said Dr. Laura Riley, chair of obstetrics and gynecology at Weill Cornell Medicine in New York City.

Specialists in her field haven’t really started talking about how to communicate with women about the vaccine, said Riley, who chairs the immunization group at the American College of Obstetricians and Gynecologists.

“Everyone’s been waiting to see if it gets approved,” she said. “The education has to start soon, but it’s hard to roll out education before you roll out the shot.”

This story comes to GPB through a reporting partnership with Kaiser Health News.