What Is RSV Sickness? Symptoms, Risks, and Care

Respiratory syncytial virus, or RSV, is one of the most common respiratory infections on the planet, and nearly every child catches it before their second birthday. For most healthy older children and adults, it feels like a bad cold. But for infants, premature babies, older adults, and people with chronic heart or lung disease, RSV can escalate into serious lower respiratory illness, hospitalization, and in some cases, death. Despite its prevalence, RSV has only recently gained the kind of public attention that flu and COVID receive, partly because effective vaccines and preventive antibodies have arrived just in the last couple of years.

How RSV Gets Into Your Body

RSV spreads through respiratory droplets, either by direct contact with an infected person or by touching contaminated surfaces and then touching your face.¹ The virus enters your body mainly through the eyes and nose rather than the mouth, which is why hand-to-face contact is such an efficient route of infection.² RSV does not travel long distances through the air the way measles does. It relies on large droplets and close contact, which is why outbreaks thrive in settings like daycares, hospital wards, and households with young children.

One thing that makes RSV tricky in hospitals and homes is that it can survive on hard surfaces for hours. Doorknobs, bedrails, and countertops can all serve as sources of infection. This is a major reason why hand hygiene is the single most emphasized preventive measure during RSV season, especially around infants and elderly family members.²

What RSV Symptoms Look Like

In most healthy adults and older children, RSV looks and feels like the common cold: runny nose, cough, mild fever, sore throat, maybe some fatigue. These symptoms typically peak around day four or five and clear up within a week or two. The trouble is that RSV is clinically indistinguishable from a dozen other respiratory viruses at this stage, so many people have RSV without ever knowing it.

In infants and young children, the picture can change fast. RSV has a particular affinity for the small airways of the lungs, where it damages the lining cells and triggers inflammation, mucus production, and swelling. This is what leads to bronchiolitis, which is the hallmark illness of RSV in babies.³ Signs to watch for include rapid or labored breathing, wheezing, flaring nostrils, a caving-in of the chest between the ribs with each breath, poor feeding, and unusual irritability or lethargy. In very young infants, particularly those under two months, apnea (brief pauses in breathing) can be an early and alarming sign of RSV before any other respiratory symptoms appear.

In older adults, RSV tends to present with cough, wheezing, and shortness of breath that can be mistaken for a flare-up of chronic obstructive pulmonary disease (COPD) or heart failure. The range of severity is wide, from mild symptoms that resolve at home to acute pneumonia and respiratory distress requiring hospitalization.⁴

Who Faces the Greatest Risk

The groups most vulnerable to severe RSV illness are infants (especially those born premature), older adults, and people with underlying heart or lung conditions. The reasons differ by group, but they all converge on the same basic problem: small or compromised airways, an immature or weakened immune system, or both.

Premature infants are particularly susceptible because their lungs have not fully developed. Lung maturity occurs around the 37th week of pregnancy, so babies born earlier have fewer and narrower air passages, lower lung volume, and reduced airflow capacity.⁵ Since much of the damage RSV causes comes from airway obstruction due to inflammation and sloughing of damaged cells, babies with the smallest airways are hit hardest. On top of that, premature infants miss out on the transfer of protective antibodies from the mother that normally happens in the final weeks of pregnancy, leaving them with fewer defenses against the virus.⁵ Their immune systems are also less developed in terms of complement function and the activity of white blood cells that help clear infections.⁶

For older adults, the combination of aging immune systems and the increased burden of chronic diseases like COPD and congestive heart failure creates a dangerous setup. RSV can trigger exacerbations of these underlying conditions, and hospitalized older adults with pre-existing cardiovascular disease have a substantially higher chance of experiencing acute cardiac events during RSV infection. One study found that about a third of hospitalized older adults with underlying cardiovascular disease experienced an acute cardiac event during RSV illness, compared to roughly one in twelve without heart disease.⁷ Acute heart failure was by far the most common cardiac complication in that group.

How RSV Is Diagnosed

Because RSV symptoms overlap so heavily with other respiratory viruses, you cannot diagnose it by symptoms alone. Rapid antigen detection tests exist and are commonly used in emergency departments and clinics. A large meta-analysis found these rapid tests catch about 80% of true RSV cases while correctly ruling it out about 97% of the time.⁸ That means the tests are quite good at confirming RSV when they say positive, but they miss roughly one in five cases. The gold standard for accuracy is PCR testing, which picks up viral genetic material and catches more infections, though results take longer.

In practice, whether your doctor tests for RSV specifically depends on context. For a healthy adult with cold symptoms, there is usually no reason to test because the management is the same regardless. Testing matters more when the result changes what happens next, such as in a hospitalized infant where RSV confirmation can guide isolation precautions and prevent spread to other vulnerable patients, or in an older adult where distinguishing RSV from bacterial pneumonia affects treatment decisions.

RSV Versus Other Winter Viruses

RSV, influenza, and a less well-known virus called human metapneumovirus (hMPV) all circulate during the colder months and can cause similar respiratory illness in children. But they do have some distinguishing patterns. In hospitalized children, RSV tends to cause bronchiolitis more often, while hMPV is more frequently associated with pneumonia and tends to strike slightly older kids.⁹ Influenza is more likely to bring high fever. Both hMPV and RSV cause wheezing and low oxygen levels at similar rates, and both do so more often than influenza.¹⁰ None of these distinctions are reliable enough to make a diagnosis without a test, but they help explain why your doctor might suspect one virus over another based on the clinical picture.

Treating RSV at Home and in the Hospital

There is no antiviral medication approved for routine RSV treatment. For most people, RSV care is supportive: fluids, rest, fever management, and nasal suctioning for congested babies. This sounds frustratingly passive, but it reflects the reality that the body’s immune system clears RSV on its own in the vast majority of cases.

When RSV leads to hospitalization, the main interventions are ensuring adequate nutrition (many babies with labored breathing struggle to feed) and providing supplemental oxygen when blood oxygen levels drop.¹¹ For infants who need more respiratory support, high-flow nasal cannula therapy has become a widely used tool. It delivers warmed, humidified air at higher-than-normal flow rates, which helps keep the small airways open and reduces the effort of breathing.¹² In randomized trials, high-flow nasal cannula has performed comparably to continuous positive airway pressure (CPAP) masks in reducing breathing rate and carbon dioxide levels, with the added benefit of being more comfortable and better tolerated by infants.¹³

One common misconception is that antibiotics help with RSV. They do not, because RSV is a virus. However, RSV infection can pave the way for a secondary bacterial pneumonia by damaging the airway lining, disrupting the normal clearance mechanisms, and suppressing parts of the immune response. RSV has been shown to enhance bacterial adhesion by common pathogens and reduce the ability of immune cells to clear bacteria.¹⁴ So while antibiotics are not part of RSV treatment itself, they may become necessary if a bacterial co-infection develops.

RSV and the Risk of Childhood Asthma

One of the most concerning long-term consequences of RSV is its link to recurrent wheezing and asthma in children. Studies have reported that roughly 40% of children with a history of bronchiolitis go on to develop childhood asthma.¹⁵ Whether RSV directly causes asthma or whether children who are genetically predisposed to asthma are simply the same children who get severe RSV remains a genuinely open question in pediatric medicine.¹⁶

A large study published in The Lancet tried to tease this apart by comparing children who were infected with RSV during infancy to those who were not. Among children without RSV infection during infancy, about 16% had current asthma at age five, compared to 21% of those who did have an RSV infection. Avoiding RSV in infancy was associated with a 26% lower risk of asthma at age five, and the researchers estimated that about 15% of childhood asthma cases could theoretically be prevented by keeping babies from getting RSV.¹⁷ That is a meaningful fraction, though it also tells you that the majority of childhood asthma has other drivers. Still, the asthma connection is one of the strongest arguments for preventing RSV in infancy even when the acute illness itself might not seem catastrophic.

Prevention With Vaccines and Monoclonal Antibodies

For decades, there was no vaccine against RSV, a story rooted in a disastrous trial in the 1960s. Infants who received a formalin-inactivated RSV vaccine not only failed to gain protection but developed a more severe form of the disease when they later encountered the wild virus. Hospitalizations were frequent, and two toddlers died.¹⁸ That catastrophe set the field back decades and made regulators extremely cautious about any RSV vaccine candidate.¹⁹

The breakthrough came from understanding the structure of the virus’s fusion protein (the “F protein”), which is the key molecule RSV uses to fuse with and enter your cells.²⁰ Researchers discovered how to stabilize the F protein in its “prefusion” shape, the form it takes before it has triggered cell entry, which turned out to elicit far stronger protective antibodies than the post-fusion form used in the failed 1960s vaccine. This insight underpins all three RSV vaccines now available for older adults, as well as the maternal vaccine and the monoclonal antibody given to infants.

Vaccines for Older Adults

Three vaccines are approved for adults aged 60 and older: Arexvy, Abrysvo, and mResvia. In clinical trials, Arexvy reduced RSV-related hospitalizations by roughly 60 to 65%, Abrysvo showed about 58 to 63% efficacy, and mResvia demonstrated 55 to 58% efficacy against RSV illness.²¹ All three produced five- to sevenfold increases in neutralizing antibodies that lasted up to 12 months. Side effects were generally mild: injection-site pain in roughly a quarter to a third of recipients, systemic symptoms like fatigue and headache in under 10 to 11%, and serious adverse events in less than 1%.²¹

Protecting Infants

Because you cannot safely vaccinate newborns against RSV, protection for the youngest babies comes through two routes: maternal vaccination and a monoclonal antibody called nirsevimab. Abrysvo is approved for pregnant individuals and works by transferring antibodies across the placenta to the baby before birth. Timing matters: when the vaccine is given at least five weeks before delivery, the transfer of antibodies to the baby is substantially more efficient than when given closer to the due date.²² Maternal vaccination has shown about 68 to 72% protection against infant RSV hospitalization.²¹

Nirsevimab is a long-acting monoclonal antibody given as a single injection to babies, either shortly after birth or before their first RSV season. A meta-analysis of randomized trials found it reduced RSV-related hospitalization by about 81% and severe RSV infection by about 77%, with no increase in adverse events.²³ After a single dose, nirsevimab-boosted antibody levels remain well above baseline throughout a typical five-month RSV season and stay elevated at least sevenfold above pre-dose levels through about a year.²⁴ Current recommendations generally advise either maternal vaccination or nirsevimab for the infant, not both, since either approach provides strong protection on its own.

How the Pandemic Changed RSV Season

The COVID-19 pandemic’s lockdowns, mask mandates, and school closures suppressed RSV transmission dramatically during 2020 and into 2021. When those measures lifted, RSV came roaring back in unusual ways. The first post-pandemic wave hit at atypical times and with altered intensity in many countries, though by the second and third seasons, patterns began to settle back toward normal.²⁵

In Japan, for example, the peak of RSV hospitalizations shifted from August (before the pandemic) to March in both 2023 and 2024. The age distribution also changed: during 2021 and 2022, a notably larger proportion of hospitalized children were two years old or older, likely because many of them had missed their first natural RSV exposure during lockdowns and were encountering the virus for the first time at an older age than usual.²⁶ These shifts have been a headache for public health planning, since the timing of nirsevimab doses and the readiness of hospital wards depend on knowing when RSV season will hit. The seasonal pattern appears to be re-stabilizing, but epidemiologists are still tracking whether it has permanently shifted in some regions.

The Global Burden Falls Unevenly

RSV is not just a nuisance of wealthy-country winters. A systematic analysis estimated that more than 95% of RSV-related acute lower respiratory infections in children under five, and more than 97% of RSV-attributable deaths in that age group, occur in low- and middle-income countries.²⁷ Sub-Saharan Africa bears a disproportionate share of this burden.²⁸ The disparity is driven by limited access to hospital-level respiratory support, fewer healthcare workers, delayed care-seeking, and the near-total absence of the new preventive tools in the regions that need them most.

Even in high-income countries, the economic toll is substantial. In the United States alone, RSV in adults aged 60 and older accounts for an estimated $6.6 billion in annual economic burden. Direct medical costs make up about $2.9 billion of that, and although only about 4% of RSV cases in this age group require hospitalization, those hospitalizations account for 94% of the direct medical spending. The remainder comes from lost productivity: roughly 7.9 million days of lost work per year.²⁹ These figures help explain why RSV has finally attracted serious attention from vaccine developers and health agencies after decades of relative neglect.

The Search for Antiviral Drugs

While the prevention story has been transformed by vaccines and nirsevimab, the treatment landscape remains sparse. There is no widely approved antiviral drug for RSV, and care is still fundamentally supportive. But research is active. Two major viral processes are the main targets: the fusion step, where the virus enters cells, and the replication machinery inside the cell that copies the viral genome.³⁰ Several compounds targeting these steps have reached clinical trials. Small molecules that block the F protein from interacting with cell membranes have shown the ability to inhibit viral entry and infection in laboratory settings.³¹ Whether any of these candidates will prove safe and effective enough to reach routine clinical use remains an open question, but the pipeline is more active than at any point in the virus’s history.