Differing immune responses in infants may explain increased severity of RSV over SARS-CoV-2

Study finds infants’ immune systems respond very differently to the two viruses, with important treatment implications.

2026-02-25

(Press-News.org) (MEMPHIS, Tenn., Farmington, Conn. – February 25, 2026) Young infants hospitalized with respiratory syncytial virus (RSV) often become much sicker compared to those infected with SARS-CoV-2, the virus that causes COVID-19. In a study published today in Science Translational Medicine, scientists from St. Jude Children’s Research Hospital and The Jackson Laboratory (JAX) report that the two respiratory viruses trigger different immune responses. Those differences might explain why these two diseases have different clinical outcomes and require different treatment strategies.

During the COVID-19 pandemic, physicians observed that infants admitted with RSV infection often had more severe symptoms than those hospitalized with SARS-CoV-2, despite both being respiratory RNA viruses. To understand these differences, the researchers compared the immune responses of infants hospitalized with either virus to those of healthy infants at a single-cell level. Measurements of proteins, genes and epigenetic signatures in the blood revealed the specific immune cells and signals central to these differences.

“We showed, for the first time, that two similar respiratory viruses, RSV and SARS-CoV-2, cause very different types of immune dysregulation in young infants,” said co-corresponding author Octavio Ramilo, MD, St. Jude Department of Infectious Diseases chair. “The host response differs depending on the infecting virus at the chemical, cellular and even epigenetic level.”

The researchers found that severe RSV in infants was linked to unexpectedly low levels of systemic inflammation and a poorly coordinated early immune response, primarily by a special set of immune cells called natural killer cells. This pattern contrasts with the hyperinflammatory immune response profile observed in infants with SARS-CoV-2 infection.

“What surprised us most was that the antiviral responses looked similar at first glance, but when we examined how immune genes were regulated, we saw striking differences,” said co-corresponding author Duygu Ucar, PhD, Professor at JAX. “RSV appears to reprogram parts of the infant immune system at the epigenetic level; which are molecular switches that control how genes are turned on or off.”

“These changes may help explain why RSV can lead to more severe disease and possibly influence how the immune system responds in the future,” Ucar concluded.

RSV suppresses immune response, increasing its severity

To find these differences, the researchers compared immune cells and proteins from blood samples derived from 19 infants hospitalized with RSV infections, 30 infants hospitalized with SARS-CoV-2 infections, and 17 healthy age-matched infants. Most infants in the study were around 2 months old.

Comprehensive single-cell analysis of the infants’ immune responses revealed that both viruses cause a similar rise in most interferons, antiviral molecules that interfere with viruses, but the analysis also revealed drastic differences.

“Most strikingly, we saw infants with RSV had significantly fewer numbers of natural killer cells, compared to those with SARS-CoV-2 infections,” said co-first author Asunción Mejías, MD, PhD, MsCS, St. Jude Department of Infectious Diseases. “In those patients, these cells also made less interferon-gamma, a key molecule to defend against viruses, which was strongly correlated with disease severity.”

“Integrating single cell technologies using advanced computational methods enabled us to not only identify immune response signatures in specific immune cell types but also associate gene expression with potential epigenetic regulators,” said co-first author Asa Thibodeau, PhD, Associate Computational Scientist at JAX. “Understanding immune differences at the transcriptional and epigenetic level will guide future studies and better treatments.”

The RSV response was also marked by lower interferon-gamma expression and reduced activity of key inflammatory signals (IL-1B, NF-KB) that normally help fight infection.

Providing clinical guidance through contrast with SARS-CoV-2

In contrast to RSV, SARS-CoV-2 generally causes significant immune dysregulation across multiple cell types. The researchers observed a significant increase in many pro-inflammatory molecules in these infants, such as TNF alpha and NF-κB activity. Clinically, this may explain why anti-inflammatory treatments, such as steroids, help some patients with severe COVID-19, while they have not helped patients with RSV, and may even be harmful.

“One very practical implication of our work is that we should not routinely give steroids to infants with RSV,” Mejías said. “RSV is already immunosuppressive; giving steroids that also suppress immunity may further impair the natural killer cell response combating the virus.”

RSV remains the primary cause of infant hospitalizations and the number two cause of infant mortality worldwide. The study’s results and methodology provide a blueprint for better understanding infant immunity in general.

“Globally, five million children die before the age of 5, half occurring in the first months of life due to infection, before vaccines are given,” Ramilo said. “With the tools we have developed, we have shown that we can start to uncover what’s happening in that early immunological window to begin improving those odds.”

Authors and funding

The study’s other co-corresponding author is Jacques Banchereau, of The Jackson Laboratory. The study’s other authors are Djamel Nehar-Belaid, Radu Marches, Giray Eryilmaz and Silke Paust, The Jackson Laboratory; Zhaohui Xu, Steven Josefowicz and Virginia Pascual, Weill Cornell Medicine and Bart Jones and Marie Wehenkel, St. Jude.

The study was supported by grants from the National Institutes of Health (U01 AI131386, U19 AI168632 and U01 AI165452) and the American Lebanese Syrian Associated Charities (ALSAC), the fundraising and awareness organization of St. Jude.

St. Jude Media Relations Contact

Michael Sheffield
Desk: (901) 595-0221
Cell: (901) 379-6072
michael.sheffield@stjude.org
media@stjude.org

The Jackson Laboratory Media Contact

Roberto Molar

202-765-5144

roberto.molar@jax.org

St. Jude Children's Research Hospital

St. Jude Children’s Research Hospital is leading the way the world understands, treats, and cures childhood catastrophic diseases. From cancer to life-threatening blood disorders, neurological conditions, and infectious diseases, St. Jude is dedicated to advancing cures and means of prevention through groundbreaking research and compassionate care. Through global collaborations and innovative science, St. Jude is working to ensure that every child, everywhere, has the best chance at a healthy future. To learn more, visit stjude.org, read St. Jude Progress, a digital magazine, and follow St. Jude on social media at @stjuderesearch.

About The Jackson Laboratory

The Jackson Laboratory (JAX) is an independent, nonprofit biomedical research institution with a National Cancer Institute-designated Cancer Center. JAX leverages a unique combination of research, education, and resources to achieve its bold mission: to discover precise genomic solutions for disease and empower the global biomedical community in the shared quest to improve human health. Established in Bar Harbor, Maine in 1929, JAX is a global organization with nearly 3,000 employees worldwide and campuses and facilities in Maine, Connecticut, New York, California, Florida, and Japan. For more information, please visit www.jax.org.

END

ELSE PRESS RELEASES FROM THIS DATE:

The invisible hand of climate change: How extreme heat dictates who is born

2026-02-25

We already know that climate change brings extreme weather, but new research reveals it is also rewriting human demography. According to a massive new study published in the Proceedings of the National Academy of Sciences (PNAS), exposure to extreme heat during pregnancy significantly alters the human sex ratio at birth, resulting in fewer baby boys. By analyzing high-resolution temperature data alongside 5 million live births in 33 sub-Saharan African countries and India, an international team of researchers — including Portland State University demographer Joshua Wilde — discovered ...

Surprising culprit leads to chronic rejection of transplanted lungs, hearts

2026-02-25

Despite advances in the field of organ transplantation, long-term organ rejection that can become apparent a decade or more after a heart or lung transplant remains a common problem for patients. This chronic organ failure has long been attributed exclusively to the recipient’s immune system attacking the foreign organ over time. Now, a study led by researchers at Washington University School of Medicine in St. Louis shows that chronic organ rejection may instead be triggered by the disruption of lymphatic vessels — an important drainage system throughout the body — ...

Study explains how ketogenic diets prevent seizures

2026-02-25

A ketogenic diet — one that is high in fat and extremely low in carbohydrates — has been known for decades to reduce seizures in some epilepsy patients. But how the highly restrictive diet achieves these effects has not previously been understood. Researchers at Washington University School of Medicine in St. Louis have now shown in mice that the diet causes physical changes in brain cells affecting how they send information to one another, dampening the strength of the signals between them. This quieter neural landscape might explain how the diet calms the overactive ...

New approach to qualifying nuclear reactor components rolling out this year

2026-02-25

Contact: Kate McAlpine, 734-647-7087, kmca@umich.edu ANN ARBOR—A thousand times faster than conventional testing, an ion beam approach to qualifying materials for use in the cores of advanced nuclear reactors is advancing through stages of approval by the industry standards organization ASTM. The methodology, developed with leadership by University of Michigan Engineering, will be presented at a special event hosted by the Electric Power Research Institute, March 10-11 in Charlotte, North ...

U.S. medical care is improving, but cost and health differ depending on disease

2026-02-25

February 25, 2026 – SEATTLE, Wash. – Over two decades, medical care improvements increased health spans in the U.S. by 1.3 years and medical spending by $234,000 per person over their lifetime – or about $182,000 per additional healthy year of life gained – when measured from birth. These are among the key findings in a new in-depth national study published today in Value in Health. Researchers examined how improvements in medical care changed health-adjusted life expectancy (HALE) and lifetime health care spending by evaluating changes in 132 causes of disease across all ages between ...

AI challenges lithography and provides solutions

2026-02-25

The 2026 SPIE Advanced Lithography + Patterning conference highlighted AI, both as a challenge and a solution. A case in point was the opening plenary session, which featured presentations on high performance memory and diversified manufacturing. The challenge of AI played a large role in the first talk. The existence of ultra large AI models with trillions of parameters, up from billions a few years ago, is improving AI capabilities. Those enormous models, though, pose a problem because they demand higher performing chips. At one time, the limitation was processing power, but that’s no longer the case. “The ...

Can AI make society less selfish?

2026-02-25

The Care Bears taught a generation of kids that sharing is caring, but few carried this principle into adulthood. Researchers at Michigan State University have found a new angle to promote cooperation — artificial intelligence (AI). The results of this study are published in npj Complexity. “Cooperation is everywhere in nature,” said Christoph Adami, professor at Michigan State University and senior author on the study. “But the mathematics of how cooperation can persist is not easy to understand.” The project revolves around the concept of the “tragedy of the commons” ...

UC Irvine researchers expose critical security vulnerability in autonomous drones

2026-02-25

Irvine, Calif., Feb. 25, 2026 — University of California, Irvine computer scientists have discovered a critical security vulnerability in autonomous target-tracking drones that could have far-reaching implications for public safety, border security and personal privacy. The UC Irvine team demonstrated how attackers could use an ordinary umbrella to manipulate drones, drawing the aircraft close enough to capture them or cause them to crash. The researchers developed a novel physical-world attack framework that they call FlyTrap. It exploits deficiencies in camera-based, ...

Changes in smoking status and their associations with risk of Parkinson’s, death

2026-02-25

EMBARGOED FOR RELEASE UNTIL 4:00 P.M. ET, WEDNESDAY, FEBRUARY 25, 2026 MINNEAPOLIS — A new study of smokers finds that currently smoking is associated with a lower risk of developing Parkinson’s disease, but quitting smoking was associated with a lower risk of death. The study was published on February 25, 2026, in Neurology®, the medical journal of the American Academy of Neurology. The study does not prove that smoking prevents Parkinson’s; it only shows an association. “The severe ...

In football players with repeated head impacts, inflammation related to brain changes

2026-02-25

EMBARGOED FOR RELEASE UNTIL 4:00 P.M. ET, WEDNESDAY, FEBRUARY 25, 2026 Highlights: A new study of former American football players looked at how a history of repetitive head impacts may be associated with cognitive and behavioral symptoms later in life. Researchers found higher levels of inflammation were associated with worse brain structure, which in turn was associated with poorer memory. The study does not prove cause and effect. It only shows associations. MINNEAPOLIS — In former college and professional football players, a new study has found higher levels of inflammation ...

LAST 30 PRESS RELEASES:

Meningococcal B vaccination does not reduce gonorrhoea, trial results show

AAO-HNSF awarded grant to advance age-friendly care in otolaryngology through national initiative

Eight years running: Newsweek names Mayo Clinic ‘World’s Best Hospital’

Coffee waste turned into clean air solution: researchers develop sustainable catalyst to remove toxic hydrogen sulfide

Scientists uncover how engineered biochar and microbes work together to boost plant-based cleanup of cadmium-polluted soils

Engineered biochar could unlock more effective and scalable solutions for soil and water pollution