The CDC Is Squandering the Breakthrough RSV Vaccine

When a new RSV vaccine for pregnant people arrived last fall, Sarah Turner, a family-medicine physician at Lutheran Hospital, in Indiana, couldn’t help but expect some pushback. At most, about half of her eligible pregnant patients opt to get a flu vaccine, she told me, and “very few” agree to the COVID shot.

But to Turner’s surprise, patients clamored for the RSV shot—some opting in even more eagerly than they did for Tdap, which protects newborns against pertussis and had previously been her easiest sell. For once, expectant parents were the ones starting conversations about immunizations.

Each year in the U.S., respiratory syncytial virus hospitalizes an estimated 58,000 to 80,000 kids under the age of 5; the risks are highest for infants, for whom the virus is “enemy No. 1,” says Sallie Permar, an immunologist and pediatrician in chief at NewYork-Presbyterian/Weill Cornell Medical Center. But this past season marked the first time that the U.S. had two tools that could substantially shrink that toll: a vaccine for pregnant people, who can then pass antibodies to their child, and a monoclonal antibody, known as nirsevimab, that is given directly to infants. Their arrival feels akin “to the end of polio,” Anne-Marie Rick, a pediatrician and clinical researcher at Children’s Hospital of Pittsburgh, told me: With both shots in widespread use, the risks of winter illness could forever look different for the youngest Americans.

But some experts worry that these powerful shots are being squandered. The CDC’s seasonal recommendations governing their use may simply be “too strict,” Permar told me. In keeping with those guidelines, many practices stopped giving the maternal vaccine at the end of January; the main window for administering the monoclonal antibody is expected to close at the end of this week. The next eligibility windows won’t open for months. The U.S has two brand-new shots that protect extraordinarily well against a deadly respiratory virus—and that people actually want to take—and it is holding them back.

The guiding principle behind the CDC’s recommendations has logic to it. RSV is a seasonal virus, and both injections are thought to offer protection for about six months. For the maternal vaccine, which is administered between 32 and 36 weeks of pregnancy, the clock on the baby’s protection starts after birth. So if a pregnant person gets the vaccine in June—outside of the CDC’s recommended window—and has their baby in July, their child may be vulnerable again come February, before RSV season typically ends. In theory, spring and summer infants might be better protected by getting nirsevimab starting in October, when RSV usually arrives. Current guidelines also require a choice between the two options: Most infants that benefit from maternal vaccination are not eligible to also receive nirsevimab.

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This past season, though, nirsevimab was in severely short supply—in large part because drug companies seem to have underestimated demand, William J. Muller, a pediatric-infectious-disease expert at Northwestern who helped trial the monoclonal antibody, told me. Many hospital systems also balked at the cost of the new drug, which is pricier than the maternal vaccine, wasn’t yet bundled into the expense of delivering infants, and wasn’t consistently covered by insurance. The shortfalls became so dire that Sanofi, nirsevimab’s manufacturer, stopped taking new orders for certain doses of the monoclonal antibody as early as October. The CDC issued a health alert, calling on providers to restrict administration of those doses to only the highest-risk infants. “In our hospital system, we had some for the NICU babies, and that was literally it,” Turner, of Lutheran Hospital, told me.

Nirsevimab should be more available this year: Spokespeople from AstraZeneca and Sanofi told me that the companies are “confident we will meet the global demand” for the antibody in 2024. But last year set quite a low bar. And when the window for administration opens in October—potentially already coinciding with RSV’s rise—supplies could go fast, as parents who haven’t been able to get shots for themselves or their babies rush to catch up, Grace Lee, a pediatrician at Stanford, who advised the CDC on its RSV guidance, told me. (The CDC did not respond to a request for comment.) Opening the administration window earlier for either the vaccine or the monoclonal antibody could ease that burden: The U.S. starts immunizing people against the flu well ahead of the season’s start, Lee said, because “it’s just not feasible to vaccinate the entire U.S. population in a week.”

For several years, too, “RSV has been on the move,” Permar told me, thanks in large part to pandemic mitigations. The virus was virtually absent in 2020, only to come roaring back for a bizarrely early season that began during the summer of 2021 and had mostly concluded by the end of January 2022. In the past two seasons, the virus has also arrived somewhat early, starting with a September rise. If that pattern holds, waiting until September to vaccinate pregnant people or until October to immunize infants might leave many newborns more vulnerable than they need to be for weeks or months.

Many experts do anticipate that RSV’s pattern will quickly settle back to its norm. Over the decades, its consistency “has been remarkable,” says Sarah Long, a pediatrician at Drexel University who advised the CDC on its guidelines for both new RSV interventions. But even in more predictable years, RSV transmission varies across regions—sometimes kick-starting during the summer in the South and lingering until spring further north. The recommendations “can’t be a one-size-fits-all” across the U.S., says Shabir Madhi, a vaccinologist at the University of the Witwatersrand, in South Africa, who helped lead clinical trials of the maternal vaccine. These are judgment calls: France opens its nirsevimab window earlier than the U.S.; Belgium will allow some pregnant people to receive a vaccine as early as the spring. The U.K. is weighing whether to offer both injections at any time of year.

One argument for the current seasonal window is that giving a vaccine or a monoclonal antibody injection too early might mean recipients miss out on protection at the end of the season, Karen Acker, a pediatrician at Weill Cornell, told me. But Permar and others are hopeful that the effects of the new RSV interventions might last longer than five or six months, which is about when clinical trials stopped directly testing their effects. Early data for nirsevimab, for instance, suggests that a little bit of protection may even trickle into subsequent seasons, Muller told me.

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RSV is also of greatest threat to children within the first few months of life, when their respiratory tracts are still tiny and developing. Given the choice between offering the maternal vaccine a little early—which could leave an older infant a bit more vulnerable at the season’s end—and waiting to administer nirsevimab to a young infant after RSV season has started, the former might actually be the safer strategy. Plus, summer babies who don’t get nirsevimab at the hospital are less likely to get it later, especially if their parents aren’t regularly taking them to see a pediatrician. Giving a shot on the early side is better than never giving one all, Joshua Salomon, a health-policy researcher at Stanford, told me.

In theory, the CDC’s guidelines do make room for adjustments in administration windows, in accordance with local RSV trends. But those decisions can be difficult to execute when providers have to place orders ahead of time and store vials in limited space. So far, many doctors’ offices and hospitals have stuck to the months outlined by the CDC guidance. “The cutoff dates have been taken very dogmatically,” Rick told me. At the start of the past season, infants just one day over the recommended dosing age of eight months or younger were denied nirsevimab, Turner told me. Then, a lot of providers simply stopped offering the maternal vaccine after January 31, or simply ran out.

When both the need and the enthusiasm for a vaccine or drug is strong, taking every opportunity for protection makes sense. Several experts I talked with supported wider windows; Permar thinks the U.S. should even consider offering the maternal vaccine year-round. To her mind, restrictions regarding both seasonality and gestational age too strongly limit the chances that a baby will be protected. Some providers also noted that, given all the uncertainties, they would recommend the maternal vaccine as primary defense, leaving nirsevimab as the backup—simply because the vaccine can be delivered first. A maternal shot can set babies up with protection from the moment of birth, a sort of insurance policy that can guard against nirsevimab supply or delivery issues. A wider window of vaccine eligibility might not be a perfect solution. But it could get more infants protected when they most need it—putting to best use a shot that people are actually willing to get.