Every winter, pediatric wards fill with infants struggling to breathe, their small chests retracting with each labored breath from the inflammation and obstruction that respiratory syncytial virus (RSV) causes in their airways. 

RSV is the leading cause of hospitalization in US infants. For decades after we developed effective vaccines against other childhood infections, RSV remained unconquered. We could treat symptoms, offer oxygen, and wait, but we could not reliably prevent infection. Older adults faced a quieter version of the same problem, coming in with "viral pneumonia" and heart failure that, when we tested, often turned out to be RSV.

That just changed. The transformation happened so quickly that many haven't grasped its magnitude.

Our recent systematic review in the New England Journal of Medicine, analyzing more than 500 studies across respiratory viruses, confirms what frontline clinicians have recently been witnessing: we can now prevent a large share of severe RSV disease. These aren't marginal tweaks. The new preventive strategies reduce hospitalizations by roughly 70% to 85%, representing one of the largest single advances in respiratory virus prevention in decades.

Consider what's already happening. Madrid's pediatric intensive care units report around 90% fewer RSV admissions. Chile's national program, reaching over 90% coverage with the infant antibody, saw hospitalizations drop by about three-quarters. These are observed reductions, not projections.

The evidence converges

The consistency across studies is remarkable. Multiple countries implementing nirsevimab (Beyfortus), the long-acting antibody given to infants, report roughly 80% effectiveness against hospitalization. 

Vaccination during pregnancy shows about 70% to 80% effectiveness in protecting newborns through antibody transfer. For adults over 60, vaccines demonstrate roughly 75% real-world effectiveness against RSV hospitalization. This reproducibility across different healthcare systems confirms these tools work reliably beyond controlled trials.

In the United States, early data suggest that a substantial proportion of infants now have some protection through either maternal vaccination or the antibody shot. That's notable for interventions just entering widespread use.

How science solved it

The path included devastating setbacks. 

A 1960s vaccine trial ended tragically when vaccinated children developed what scientists call "enhanced respiratory disease," becoming much sicker when they later encountered RSV than if they had never been vaccinated. Among infected vaccinees, about 80% required hospitalization versus 5% of controls, and two children died. That failure stalled RSV vaccine development for decades.

The breakthrough came from understanding RSV's structure at the molecular level. Scientists discovered that the virus's fusion protein exists in two shapes. The stable form generates weak immunity, but the unstable prefusion form contains unique sites that trigger powerful protective antibodies. Stabilizing this structure took years of engineering.

Separately, researchers extended antibody protection from weeks to months by modifying how antibodies interact with the body's recycling systems. One injection now covers an entire RSV season.

Both success and challenges

Clinicians describe RSV seasons that now feel completely different. Emergency departments report dramatically fewer infants with severe breathing problems. Hospitalizations that once overwhelmed pediatric units have declined sharply.

Yet implementation remains uneven. The infant antibody costs around $500 per dose in the United States, though most insurance covers it. Some US regions achieve near-universal protection, while others barely reach half of eligible infants. Maternal vaccination uptake remains well below half nationally, a missed opportunity given how much risk concentrates in the first three months of life.

Interestingly, some parents who decline routine vaccines accept the RSV antibody. In one hospital cohort, over 40% of parents who declined other prenatal vaccines still chose nirsevimab, perhaps because monoclonal antibodies feel different from traditional vaccines. They're pre-formed protection rather than immune system training.

Safety: real but rare risks

Large-scale analyses of millions of recipients show these interventions are safe overall. For infant strategies, no major safety concerns have emerged. 

For maternal RSV vaccination, early trial data raised concern about preterm birth when the vaccine was given over a broader gestational window. But when vaccination is given at 32 to 36 weeks' gestation as currently recommended, multiple large real-world studies have not found an increased risk of preterm birth.

For older adults, FDA analysis of more than three million Medicare beneficiaries identified approximately six to nine excess cases of Guillain-Barré syndrome per million doses. That's a real risk that should be communicated plainly. It's also rare, especially when weighed against RSV causing an estimated 60,000 to 160,000 hospitalizations annually in this age-group.

The American challenge

RSV prevention is landing in a landscape already saturated with vaccine misinformation and fatigue from the COVID-19 pandemic. Federal advisory committees now include members who actively undermine vaccine science. Social media ecosystems that fueled COVID vaccine doubt quickly pivot to new targets.

In this environment, evidence alone isn't enough. We need clear communication about what these tools do: They sharply reduce the likelihood a baby ends up in intensive care or a grandparent develops RSV pneumonia. 

They don't eliminate all infections, but they prevent a large share of the most severe disease.

Global equity test

RSV burden falls heaviest where these tools are absent. In low- and middle-income countries, RSV accounts for about 40% of respiratory hospitalizations in infants younger than six months. Roughly 97% of RSV deaths occur in these settings, where intensive care is scarce and oxygen unreliable.

The babies at highest risk of dying from RSV are precisely those who would benefit most from these interventions. Whether we find ways to ensure global access will test our commitment to translating scientific breakthroughs into health equity.

Looking forward

We've reached an inflection point. RSV, which has sickened countless children and older adults throughout human history, can now be prevented in a large share of the most severe cases. Not treated after the fact, but prevented before infection causes harm. The question isn't whether these tools work but whether we'll ensure access for all who need them.

After decades of frustration and failure, we've achieved something extraordinary: effective prevention against one of medicine's most persistent respiratory challenges. This conclusion comes from systematic review evidence backed by real-world data from multiple continents.

The transformation is real, measurable, and available now.

Dr. Scott is a clinical associate professor of infectious diseases at Stanford University School of Medicine and first author of "Updated Evidence for Covid-19, RSV, and Influenza Vaccines for 2025–2026" in the New England Journal of Medicine.

The opinions voiced in CIDRAP Op-Ed pieces are the authors' own and do not necessarily represent the official position of CIDRAP.