A recent collaborative study from researchers at University of Connecticut and Connecticut Children's explored why the 2022 outbreak of Respiratory Syncytial Virus (RSV) appeared unusually severe in children. RSV is a common respiratory pathogen, and most children experience infection by the age of three years. However, the 2022–23 season was marked by an earlier-than-usual surge in cases, leading to significant strain on paediatric healthcare services.¹

The investigation was initiated by Associate Professor in the Department of Pathobiology and Veterinary Science at UConn, together with the Head of Paediatric Infectious Diseases and Immunology at Connecticut Children’s. The researchers hypothesized that genetic mutations within circulating RSV strains may have contributed to increased disease severity observed during the outbreak.²

RNA viruses such as RSV are particularly susceptible to genetic mutations because they lack the efficient proofreading mechanisms seen in human and animal cells during replication. This allows viral genomes to accumulate changes over time, potentially altering transmissibility or virulence.³ To explore this possibility, respiratory samples were collected from paediatric patients toward the end of the 2022–23 RSV season. Adult samples were also obtained in collaboration with researchers from UConn Health.

The research team compared viral genomes from patients with mild illness and those with severe disease requiring intensive medical support. Analysis identified 19 consistent mutations associated with severe paediatric RSV infection. These findings were reported in a preprint published on bioRxiv.²

Further laboratory experiments demonstrated that RSV strains carrying these mutations replicated substantially faster than strains isolated from children with milder disease. Viral replication rates were approximately 10–100 times higher in severe-disease samples under similar experimental conditions. Investigators suggested that one or more mutations affecting viral replication genes may explain this enhanced growth pattern.²

Rapid viral replication is widely considered an indirect marker of increased virulence because higher viral loads may contribute to more severe clinical manifestations and facilitate transmission.³ The authors believe that identifying mutation patterns linked to severe disease may eventually help clinicians predict which children are at greater risk for complications and may benefit from closer monitoring or earlier supportive interventions.

The researchers also highlighted the need for ongoing surveillance to determine whether recently introduced RSV preventive strategies, including maternal vaccination and monoclonal antibody prophylaxis for infants, could influence viral evolution by exerting selective immune pressure on circulating strains. Although these preventive measures reduce disease burden, there is scientific interest in understanding whether RSV may adapt in response to increasing population immunity.⁴

The study additionally examined RSV infection in older adults, another high-risk population. Researchers noted that interpretation of disease severity in adults is more challenging because comorbid conditions frequently complicate infection outcomes. Collaborative studies with regional hospitals are continuing to evaluate these factors further.

Although the current study involved a relatively small sample size, the investigators have continued collecting RSV isolates across subsequent seasons to better understand long-term viral evolution and patterns of disease severity. The project also emphasized the value of multidisciplinary collaboration between clinicians, laboratory scientists, and trainees in advancing infectious disease research.

References:

1. Respiratory Syncytial Virus Infection. Centers for Disease Control and Prevention. Respiratory Syncytial Virus Infection (RSV) [Internet]. Atlanta: CDC; 2024 [cited 2026 May 27]. Available from: CDC RSV Overview

2. Szczepanek S, Michelow I, Dieckhaus K, et al. Genomic mutations associated with severe respiratory syncytial virus disease in paediatric patients. bioRxiv [Preprint]. 2024. Available from: bioRxiv Preprint

3. Respiratory Syncytial Virus Infection. Hall CB, Weinberg GA, Blumkin AK, et al. Respiratory syncytial virus-associated hospitalizations among children less than 24 months of age. N Engl J Med. 2009;360(6):588-98.

4. Nirsevimab. Hammitt LL, Dagan R, Yuan Y, et al. Nirsevimab for prevention of RSV in healthy late-preterm and term infants. N Engl J Med. 2022;386(9):837-46.