Study shows a strong association between early-life RSV infection and an increased risk of asthma in childhood.A study presented at ESPID 2026 demonstrates an association between respiratory syncytial virus (RSV) infection and an increased risk of childhood asthma.
“Early-life RSV infection is strongly associated with an increased risk of asthma in childhood. Importantly, the risk persisted up to at least 12 years of age,” said Dr Giulia Dallagiacoma from Karolinska Institutet, Stockholm, Sweden, at ESPID 2026.
After adjusting for sex, prematurity, maternal BMI, small for gestational age, socioeconomic status, and smoking exposure during pregnancy, RSV infection before 2 years of age was associated with increased odds of prevalent asthma (ie, asthma at 5, 8, and 12 years of age; adjusted odds ratios [aORs], 2.61, 2.12, and 1.93, respectively). “These results imply that the risk persisted throughout childhood,” Dallagiacoma said.
This effect was similarly observed when stratifying RSV by age category, with the most pronounced effects among children infected at 12–24 months (aORs, 3.38, 2.81, and 2.09 for asthma at 5, 8, and 12 years, respectively). The corresponding aORs of RSV infection at 6–11 months were 3.16, 2.50, and 2.35, and 2.36, 1.91, and 1.8 at 0–5 months. [ESPID 2026, abstract OP-026]
Similar effects were observed when looking at RSV by disease severity. Among participants with outpatient visits, the aORs for asthma at 5, 8, and 12 years were 2.4, 1.81, and 1.46, respectively. The effects were more pronounced among children admitted to the ICU (aORs, 4.17, 3.04, and 1.95, respectively).
“We observed a clear gradient in the risk of asthma with increasing healthcare utilization and disease severity, starting with outpatient visits, increasing lengths of hospitalization, and ICU admission regardless of the length of stay,” Dallagiacoma said.
Other analyses
In the within-sibling analysis, the risk (adjusted hazard ratio [aHR]) of incident asthma (ie, asthma up to 13 years of age) in the total population was 3.45. Albeit slightly attenuated, the association remained among full siblings (aHR, 2.91), maternal half-siblings (aHR, 2.64), and paternal half-siblings (aHR, 3.03).
Among full siblings, RSV infection remained associated with an increased risk of asthma at 5, 8, and 12 years (aORs, 1.74, 1.55, and 1.38, respectively). Dallagiacoma noted that the estimates were also higher for half-siblings.
In the within-twin pair analysis, the odds (ORs) of developing asthma at 9 years were 2.18 in all twins and 2 in monozygotic twins, after adjusting for sex. In dizygotic twins, the OR was 4.06.
“The persistent associations in the co-sibling and co-twin analyses suggest that environmental and familial confounding are unlikely to fully explain the effect. Therefore, a causative role of RSV cannot be excluded,” Dallagiacoma said.
Unclear associations
RSV infection in infancy has been correlated with asthma development in childhood, but the nature of this relationship remains uncertain. “It is unclear whether it is a causal association or if these children are simply predisposed to both conditions through genetics and/or early-life factors,” Dallagiacoma pointed out.
As such, Dallagiacoma and her team sought to ascertain whether early-life, medically attended RSV infection causally contributes to childhood asthma, independent of shared genetic and early environmental factors, and whether the timing and the severity of infection modify the risk.
The researchers used data from the Swedish National Patient Register (NPR) of children born 2004–2022 who had an RSV diagnosis before 2 years of age (n=1,977,650). The within-sibling analysis also used data from the NPR. “This allowed us to compare children who shared genetics to different degrees and early-life factors,” Dallagiacoma noted. For the within-twin pair analysis, the investigators used data from the Swedish Twin Registry (n=46,809 twins born 1992–2014).