Among young children who contract respiratory syncytial virus (RSV) in the first 2 years of life, the risk for developing respiratory morbidity later in childhood is greater among children who contract RSV over the age of 6 months, according to study findings published in Open Forum Infectious Diseases.

Investigators studied children who contracted RSV in their first 2 years of life, exploring which perinatal and sociodemographic factors may have contributed to respiratory morbidity (ie, asthma, wheezing, or acute lower respiratory infection) later in childhood.

The investigators conducted a population-based cohort study using administrative data that included more than a quarter of a million births in Western Australia between 2000 and 2009, with follow-up through December 2012. Children with a confirmed RSV test prior to 2 years of age (n=4151) were included in analysis.

The investigators found as the child age at RSV infection increased, the likelihood of subsequent respiratory morbidity also increased. Compared with children experiencing RSV at less than 3 months of age (IR of subsequent respiratory morbidity, 16.2/1000 child-years; 95% CI, 13.5-19.4), children with first RSV episode at an older age experienced higher rates of subsequent respiratory morbidity (3 months to less than 6 months IR, 17.2/1000 child-years; 6 months to less than 12 months IR, 23.6/1000 child-years; 12 months to less than 24 months IR, 22.4/1000 child-years). 

Early RSV exposure in the first 6 months of life resulted in a relatively lower incidence of later respiratory morbidity compared with RSV exposure after 6 months of age.

Investigators also found that the highest incidence of respiratory morbidity following early-life RSV infection occurred in children 2 to less than 4 years of age (IR, 41.8/1000 child-years; 95% CI, 37.5-46.6), followed by children 4 to less than 6 years of age (IR, 13.0/1000 child-years), and children at least 6 years of age (IR, 5.7/1000 child-years).

Gestational age at birth had the largest influence on the likelihood of experiencing later respiratory morbidity; as gestational age decreased, incidence rates of subsequent respiratory morbidity increased. The highest incidence occurred among children with gestational age less than 28 weeks (IR, 50.8/1000 child-years; 95% CI, 33.5-77.2; gestational age 29 to 32 weeks IR, 30.3/1000 child-years; gestational age 33 to 36 weeks IR, 18.4/1000 child-years; gestational age at least 37 weeks IR, 18.4/1000 child-years).

Overall, the researchers identified the risk factors for subsequent respiratory morbidity as: extreme prematurity (<28 weeks, adjusted hazard ratio [aHR], 2.22; 95% CI, 1.40-3.53), low socioeconomic index (aHR, 1.76), age at first RSV episode (6 to <12 months, aHR, 1.42), and maternal history of asthma (aHR, 1.33).

In comparing respiratory morbidity in boys vs girls, the researcher found that boys testing negative for RSV in the first 2 years of life had a 1.38-times greater risk for later respiratory morbidity vs girls.  In evaluation the effect of a mother who smoked during pregnancy, the researchers found that children of mothers who smoked during pregnancy had a 1.01-times greater risk for later respiratory morbidity than children of mothers who did not smoke.

Study limitations include the use of ICD codes to identify outcomes. Additionally, not all respiratory infection-coded admissions were tested for RSV, which could have resulted in sampling bias.

“Early RSV exposure in the first 6 months of life resulted in a relatively lower incidence of later respiratory morbidity compared with RSV exposure after 6 months of age,” the study authors concluded. “Our results would support a recommendation to offer nirsevimab for children approaching their second RSV season (therefore over the age of 6 months).”

Disclosure: This research was supported by Merck Sharp & Dohme (Australia) Pty. Ltd. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

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