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Infant RSV Disease Burden and Epidemiologic Trends: Take Infant RSV Prevention to New Heights
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Activity Information

Pharmacists: 0.25 contact hour (0.025 CEUs)

Nurse Practitioners/Nurses: 0.25 Nursing contact hour

Physicians: maximum of 0.25 AMA PRA Category 1 Credit™

Released: October 20, 2025

Expiration: October 19, 2026

Joseph Domachowske
Joseph Domachowske, MD
Sharon G. Humiston
Sharon G. Humiston, MD, MPH
Pablo J. Sanchez
Pablo J. Sanchez, MD

Team Trivia! Test Your Knowledge and Take Infant RSV Prevention to New Heights

 

The Villain: Respiratory Syncytial Virus

 

All right. So I'm going to present you the villain first. The villain here for tonight is respiratory syncytial virus.

 

[00:08:44]

 

Estimated Annual RSV Burden in Infants and Young Children: United States

 

Shown here are the annual RSV burden in US infants that is less than 12 months of age. We know that RSV is consistently the leading cause of US infant hospitalization. Sound familiar?

 

Overall, approximately 10% of all infant hospitalizations are still due to RSV infection. We can finally do something about that. And the landscape is evolving. But these are the most recent numbers from the last few years.

 

Of our birth cohort, which is a little over 3.5 million every year, there are close to 2 million RSV infections, 850,000 RSV lower respiratory tract infections, bronchiolitis and pneumonia. And you can see the numbers for outpatient visits, totaling about 600,000 medically attended visits for bronchiolitis or pneumonia.

 

And we're fortunate in the US that we can support most of these babies through, but still we have about on average, about 100 deaths from RSV every year.

 

[00:09:47]

 

The Victims

 

So the victims are all of us, right? So we're going to highlight the infants and the high-risk young children for this evening. But we're infected over and over again. There's no sterilizing immunity when you get this infection. And certainly at the extremes of age, we see the highest burden of disease.

 

[00:10:05]

 

Annual RSV Burden in the US: 2024-2025 Estimates

 

If we take all ages all together and look at the entire US population, we're talking about CDC estimates for the last RSV season between 3.5 and 6.5 million outpatient visits for RSV. This is all age groups, between 190,000 and 350,000 RSV-related hospitalizations and between 10,000 and 23,000 RSV-related deaths.

 

And of course, most of those deaths, again, are in frail, elderly individuals with comorbidities. Because I already showed you, luckily, we can bring most of our infants and young kids through the infection with support.

 

[00:10:44]

 

Age-Specific Strategies for RSV Prevention

 

There are now age specific strategies for RSV prevention that target the very young and the elderly, particularly high-risk groups, especially when we talk about the elderly. But 1 of the things I want to focus on for tonight, and you'll hear this from, I think each of us tonight, is that we are no longer stratifying risk for infants. All infants, because of being infants, are at high risk for severe RSV infection. And you don't know which ones are going to end up in your offices, in your ERs or in your hospital just because they are young infants.

 

We know some of the higher risk groups, and we'll go over those for the ones more likely to end up in the hospital. But all infant protection is necessary because all infants are at risk for severe disease.

 

[00:11:38]

 

The Hero: Protection for All Infants

 

So here are the heroes, right, for tonight. We have our villains. And then we have our victims. And now we have our heroes. And we currently have available for all infant protection, both vaccines during pregnancy or long-acting monoclonal antibodies. And we'll get into these in some detail when Dr Sanchez presents his part of the discussion.

 

Nearly 70% of infants experienced their first RSV infection during their first year of life. In almost all of them, by age 2 have had RSV at least once already. So it's very high burden, very high community levels. We know about when it's coming, and we know about when it peaks. We'll talk about some of the trends regionally and locally in a little bit.

 

[00:12:32]

 

RSV-Associated Respiratory Failure in Infants and Young Children

 

When infants get RSV infection and it goes to their lower respiratory tract, we're always most concerned about those that develop lower respiratory tract symptoms of pneumonia bronchiolitis. But remember that the very youngest ones, especially less than 6 weeks of age and those that were born preterm, have a propensity to have some periodic breathing when they get RSV infection, and some of them will develop apnea. So sometimes they're admitted because of this, right? They're just having these unusual spells of periodic breathing and apnea.

 

Some of them are breathing so fast they can't coordinate their suck, swallow and eating along with staying hydrated because they’re - they're just tachypneic. They're breathing more than 80 per minute sometimes, even up to 100 per minute. It's not unusual. So dehydration secondary to RSV is also a common reason for infant hospitalization.

 

[00:13:26]

 

RSV Hospitalization Rates per Mo of Age in the United States: Timing Matters

 

Now, the majority of infants who are hospitalized are under 6 months of age, but you can see that the burden of disease continues out into the second year of life. We still have some work to do to protect those infants or those children beyond that first RSV season. These are investigational products that are being evaluated.

 

But for the first season, all infant protection is the bottom line message here. We have the opportunities to do it. We have the products. We know that they work, and you'll see how well they work in just a few minutes. We should optimize their coverage rates, optimize their use, and we will change the landscape of RSV infection in the United States and anywhere else that adopts these immune-prophylaxis regimens.

 

[00:14:18]

 

Risk Factors for Severe RSV Infection in Infants Entering Their First RSV Season

 

So I mentioned that more than 70% of infant RSV hospitalizations occur in the absence of risk factors, meaning that most of the babies that end up hospitalized with or for RSV were born at term without identifiable risk factors, except being infants.

 

You can see the risk factors on the right-hand side of this slide, including being born preterm, and some of the reasons why these represent higher risk factors: chronic lung disease, chronic lung disease of prematurity, congenital heart disease that's not yet repaired, neuromuscular disease because of suck, swallow coordination and possibility of aspirating upper airway infected content and immune deficiency.

 

And while this represents a minority of our total birth cohort, it is important to recognize when infants are at even higher risk than the general population. Between 1% and 3% of all infants born every year in the US end up in the hospital with RSV.

 

[00:15:23]

 

Burden of RSV Infection in Children Aged <5 Yr

 

Now if we look at the hospitalizations and the burden of RSV infection in kids under 5 years of age. If we focus by age groups, first looking at the less than 6-month-olds in the first bar graph, you can see that the majority of them were previously totally healthy, between 70% and 75%. 25% can be identified as having extra risk factors on top of it.

 

By the time they get to the second half of their first year of life and into their second year, up to 24 months, you can see that it's split about 50-50. So as they age even a little bit into that second year of life, the number that have predisposing conditions that we can recognize as clinicians as saying, you know, this is a kid that's probably going to end up pretty sick when they get RSV. That's because they're a little bit older. And we know what those conditions are.

 

For the 2- to 5-year olds, you can see that the majority of those sort of flips. 70% have underlying conditions, but still a third of them have no recognizable known underlying risk factors for severe infection. And they still develop lower respiratory tract infection that requires hospitalization.

 

[00:16:43]

 

Burden of Post-RSV Wheezing/Asthma

 

We know that RSV in the first year of life predisposes to recurrent wheezing. Some call it asthma, some call it postviral wheezing. I'm not sure that asthma is the same thing, but in the literature it's often used synonymously.

 

From 2010 to 2016, data from insurance claims, as you can see here, were looked at for wheezing and asthma after hospitalization for RSV during that first year of life. Matched-pairs were analyzed based on their gender, their birth, their birth year and their month, their healthcare plan, and their region of residence. And you can see that they were followed up at 2, 3, 4, and 5 years from birth to assess recurrent wheezing episodes and asthma.

 

Asunción Mejías published this just 5 years ago—less than 5 years ago.

 

[00:17:39]

 

Cumulative Incidence of Post-RSV Recurrent Wheezing/Asthma During First 5 Yr of Life

 

And here's what she found. Cumulative incidence of post-RSV recurrent wheezing during the first 5 years of life increases over time and was 2-4 times higher if you had RSV and required hospitalization in your first year of life. So it's an independent risk factor for recurrent wheezing and adds to the burden that these babies have for the public health, and, you know, all of these costs for coming back into the office for medications that they may need and for reassurance when they have these wheezing episodes.

 

[00:18:17]

 

NREVSS Dashboard for RSV: Seasonal Epidemiology

 

Now, if we turn now to the epidemiology, I'm going to call the epidemiology for RSV predictably unpredictable. We always know it's coming, right? The only time we didn't see RSV appearing as an annual epidemic was right after COVID hit and everyone was masking and social distancing, and all those nonpharmacologic interventions that we imposed on each other and on our families and our patients so to prevent the transmission of COVID. Well, it also prevented the transmission of RSV, influenza, and pretty much all other respiratory viral infections.

 

And you can see here this flat part of the curve between 2020 and 2021, that was that year where we were just blessed. We just did not see any burden of RSV. I don't think we had a single RSV hospitalization in Syracuse that particular year. There might have been one. But we know how to prevent it. It's just not practical to do that. We can't keep people at home masked and separated from each other all the time.

 

Now we have safe and effective interventions that can achieve very similar types of results. Without them, you can see that year-to-year we know the epidemics are coming. The peaks are similar. The time that the individual RSV season start each year is not precisely predictable, but you can estimate it fairly well for your region, knowing your local epidemiology, especially now that we've kind of reverted back to pre-pandemic epidemiology for most areas of the country.

 

But 1 thing I also want you to notice here is the width of each of these RSV seasons, shown here on this slide, kind of the - the - the shoulder here, the width between the shoulders is different. Some seasons last longer than others. Some start earlier and linger on. And this is also true from region to region.

 

Now, anybody from Florida knows that the RSV season starts earlier and lasts longer than pretty much anywhere else in the US. Our regional epidemiology is very important, especially when we talk about seasonal strategies for prevention. And Dr Sanchez will tell us a lot about those in just a minute.

 

[00:20:38]

 

NREVSS Dashboard for RSV: Regional Epidemiology

 

Just to drive this point home. This is a fairly complicated slide here, but you can see the map on the left dividing up the US by regions. This is those regions by Health and Human Services. And you can see on the right-hand side in the same color coding that each region has sort of different times of peak, different times when the season starts, different times when it ends.

 

In general, you can probably say that RSV typically starts around the beginning of October and continues through the end of March. But there are exceptions, and we need to be aware of them, especially when we're talking about immunoprophylaxis strategies that we have.

 

[00:21:22]

 

Key Points

 

So my key points and I'll finish up here. All infants are at risk for severe RSV disease, especially during their first infection. RSV accounts for nearly 10% of all cause infant hospitalization. Recurrent wheezing during childhood is more common among those who are infected with RSV during infancy, and precise onset and duration of annual RSV epidemics differ from year to year and from region to region.

 

[00:21:50]