Children hospitalized for respiratory syncytial virus at older ages may face a substantially higher risk of bacterial pneumonia later in childhood, according to a large population-based cohort study conducted in Sweden.
Respiratory syncytial virus (RSV) is one of the most common causes of lower respiratory tract infections in young children worldwide, accounting for an estimated 33 million infections, 3.6 million hospitalizations, and more than 100,000 deaths annually among children younger than 5 years. Previous research has linked severe early RSV infection with long-term respiratory complications such as asthma, but the relationship between age at RSV hospitalization and subsequent bacterial pneumonia has been less well understood.
To investigate this association, researchers analyzed national registry data from 1,641,746 children born in Sweden between 1998 and 2015, following them until age 5 years or until hospitalization for bacterial pneumonia, death, or emigration. The study incorporated data from multiple national registers, including the Medical Birth Register and the National Inpatient Register, and examined more than 8 million person-years of follow-up.
Overall, the cohort included 29,046 RSV hospitalizations and 8,327 hospitalizations for bacterial pneumonia.
The researchers found that the risk of bacterial pneumonia was highest shortly after RSV hospitalization and increased as the age at first RSV hospitalization increased.
Compared with children who were never hospitalized for RSV, those hospitalized between birth and 5 months of age were about five times more likely to be hospitalized for bacterial pneumonia during the first two months after RSV infection. After that period, the risk remained elevated but was lower.
The association was even stronger among children hospitalized with RSV at older ages. Children whose first RSV hospitalization occurred between 18 and 23 months of age were more than eight times as likely to be hospitalized for bacterial pneumonia during the first two months after infection, and their risk remained more than fourfold higher thereafter.
The researchers suggested that age-related differences in immune responses to RSV may partly explain the findings. Older infants and toddlers with severe RSV infection may exhibit stronger neutrophil-related immune responses, which has been proposed as one possible explanation for increased susceptibility to bacterial complications.
However, the researchers also noted that the association may partly reflect greater underlying susceptibility to respiratory infections among children hospitalized with RSV at older ages, including those with comorbidities that become more common later in infancy and early childhood.
The findings may have implications for RSV prevention strategies. Current approaches—such as maternal vaccination and long-acting monoclonal antibodies administered in early infancy—primarily protect infants during the first months of life and may not extend protection to older children who remain vulnerable to severe RSV disease.
The study has several limitations, including the inability to adjust for certain potential confounding factors such as breastfeeding, day-care attendance, or comorbidities diagnosed after the neonatal period, which may influence susceptibility to respiratory infections.
The researchers concluded that preventing RSV infections during the first two years of life could help reduce the risk of subsequent bacterial pneumonia in early childhood, highlighting potential broader benefits of RSV prevention strategies.
Disclosures can be found in the study.
Source: Acta Paediatrica