Whether their baby might end up in the hospital
Each winter, respiratory syncytial virus claims more infant hospital beds in America than any other infectious disease — a quiet, recurring toll that medicine has long struggled to interrupt. A study from the University of Pittsburgh, published in JAMA Network Open, now offers real-world confirmation that a vaccine given to mothers during pregnancy can reduce their newborns' risk of hospitalization by roughly 70 percent. The RSVpreF vaccine, approved by the FDA in 2023, works through the ancient biological covenant between mother and child — immunity passed through the placenta before a baby ever draws its first breath. What was once a season of helpless waiting has begun, at last, to look different.
- RSV hospitalizes two to three out of every hundred American infants under three months old each winter, with the most severe cases requiring oxygen or mechanical ventilation.
- Until 2023, no reliable tool existed to protect newborns from birth — leaving the most vulnerable patients with almost no medical defense during their earliest weeks of life.
- Researchers tracked real hospital admissions across two RSV seasons in western Pennsylvania, comparing vaccinated and unvaccinated mothers' infants to measure actual, not theoretical, protection.
- The data showed a 68–69 percent reduction in RSV-related hospitalizations, holding firm even for the most severe lung infections — results that matched clinical trial predictions in messy, real-world conditions.
- A four-year study running through 2027 is now tracking how long protection lasts and how it performs across multiple seasons, with findings set to shape clinical guidance and public health policy.
Respiratory syncytial virus is the leading infectious cause of infant hospitalization in the United States. In the coldest months, when the virus spreads most aggressively, some babies need oxygen; others need machines to breathe for them. For a long time, medicine had almost nothing to offer.
The RSVpreF vaccine, FDA-approved in 2023, changed the calculus. Rather than vaccinating infants directly, it is given to mothers during pregnancy — and immunity crosses the placenta, reaching the newborn before birth. Researchers at the University of Pittsburgh and UPMC have now published the first real-world evidence of what that protection looks like in American hospitals.
The study, appearing in JAMA Network Open, followed infants ninety days old or younger hospitalized with respiratory illness across western Pennsylvania during two consecutive RSV seasons. Comparing babies born to vaccinated and unvaccinated mothers, the team found that maternal vaccination reduced RSV-related hospitalization risk by roughly 68 percent — and held at 69 percent for the most severe cases requiring intensive intervention.
Lead author and UPMC pediatrician Anne-Marie Rick framed the findings in human terms: fewer infants in pediatric wards, fewer parents sleeping in hospital chairs. The results carry particular weight because they emerged not from a controlled trial but from the records of actual hospitals — a messier, more convincing proof of effectiveness.
The research team is not done. A four-year study running through 2027 will track protection across multiple RSV seasons, following infants up to six months old and measuring how long the vaccine's shield endures. The question is no longer whether the vaccine works. The question now is how long, and for whom it works best.
Respiratory syncytial virus sends more American infants to the hospital than any other infectious disease. In the coldest months, when RSV spreads fastest, roughly two or three out of every hundred babies under three months old end up admitted for treatment. Some need oxygen. Some need machines to breathe for them. Until three years ago, there was almost nothing doctors could do to stop it.
Then came the RSVpreF vaccine. The FDA approved it in 2023, and it works differently than most infant vaccines—the mother receives it during pregnancy, and her body passes protection to the newborn through the placenta. Now, researchers at the University of Pittsburgh and UPMC have published the first real-world evidence of what that protection actually means in American hospitals.
The study, published in JAMA Network Open, tracked infants ninety days old or younger who were hospitalized with respiratory illness across western Pennsylvania during two consecutive RSV seasons. The researchers compared outcomes between babies whose mothers had been vaccinated during pregnancy and those whose mothers had not. The difference was stark: maternal vaccination reduced the risk of hospitalization for RSV-caused illness by roughly 68 percent. For the most severe cases—infections that damaged the lungs badly enough to require intensive intervention—the protection held at 69 percent.
Anne-Marie Rick, the lead author and a pediatrician at UPMC Children's Hospital, framed the work around what parents actually care about. "We designed this study to focus on what matters most to families: whether their baby might end up in the hospital," she said. The numbers suggest the vaccine does exactly that. A 70 percent reduction in hospitalization is not theoretical. It means fewer cribs in pediatric wards. It means fewer parents sleeping in hospital chairs. It means infants who stay home.
The findings align with what the vaccine's clinical trials had predicted, but clinical trials and real-world hospital data are different things. Trials are controlled. Hospitals are messy. They include patients of different ages, different health backgrounds, different exposures. That these results held up in actual practice—in the records of actual infants admitted to actual hospitals—carries weight with clinicians and policymakers trying to decide whether to recommend the vaccine widely.
The research team is not finished. They are running a four-year study that will track protection across multiple RSV seasons through 2027, expanding to follow infants up to six months old and measuring how long the vaccine's shield actually lasts. Rick emphasized that these ongoing real-world observations are essential for families, doctors, and health officials trying to make decisions about how to protect the most vulnerable patients. The question now is not whether the vaccine works. The question is how long it works, and for whom it works best.
Notable Quotes
We designed this study to focus on what matters most to families: whether their baby might end up in the hospital.— Anne-Marie Rick, M.D., Ph.D., lead author and pediatrician at UPMC
Real-world data are critical for helping families, clinicians, and policymakers make informed decisions about how best to protect infants.— Anne-Marie Rick
The Hearth Conversation Another angle on the story
Why does RSV hit infants so hard when older kids and adults usually recover fine?
Newborns have almost no immune memory. Their lungs are still developing. RSV doesn't just cause a cough—it inflames the small airways so badly that babies can't move air in and out. That's why some need oxygen or a ventilator.
And the vaccine works by giving the mother antibodies that cross the placenta?
Exactly. The mother's immune system makes antibodies against RSV, and those antibodies transfer to the baby before birth. The baby is born already protected, which matters most in those first three months when RSV is most dangerous.
Why did it take until 2023 to develop this? We've had vaccines for decades.
RSV is tricky. Previous attempts to vaccate against it actually made infection worse in some cases—a phenomenon called antibody-dependent enhancement. It took a long time to design a vaccine that was both safe and effective. The RSVpreF vaccine uses a stabilized protein that avoids that problem.
So this study proves it works in the real world, not just in trials?
It shows that in actual hospitals, in actual infants, the protection holds. Sixty-eight to 69 percent effectiveness is substantial. That's not a marginal benefit.
What happens after six months? Does the protection fade?
That's what they're still studying. The antibodies the mother passes do decline over time. The researchers are tracking how long protection lasts and whether some infants lose it faster than others. That matters for deciding when and how to vaccinate.
If a mother gets vaccinated, does she also get protected?
The vaccine protects her too, but the real target is the newborn. The mother's protection is a secondary benefit. The primary goal is keeping the baby safe during those first months when RSV is most likely to cause severe disease.