Incidence of Respiratory Syncytial Virus–Associated Lower Respiratory Tract Illness in Infants in Low- and Middle-Income Regions During the Coronavirus Disease 2019 Pandemic.

Background Incidence data of respiratory syncytial virus–associated lower respiratory tract illness (RSV-LRTI) are sparse in low- and middle-income countries (LMICs). We estimated RSV-LRTI incidence rates (IRs) in infants in LMICs using World Health Organization case definitions. Methods This prospective cohort study, conducted in 10 LMICs from May 2019 to October 2021 (largely overlapping with the coronavirus disease 2019 [COVID-19] pandemic), followed infants born to women with low-risk pregnancies for 1 year from birth using active and passive surveillance to detect potential LRTIs, and quantitative reverse-transcription polymerase chain reaction on nasal swabs to detect RSV. Results Among 2094 infants, 32 (1.5%) experienced an RSV-LRTI (8 during their first 6 months of life, 24 thereafter). Seventeen (0.8%) infants had severe RSV-LRTI and 168 (8.0%) had all-cause LRTI. IRs (95% confidence intervals [CIs]) of first RSV-LRTI episode were 1.0 (.3–2.3), 0.8 (.3–1.5), and 1.6 (1.1–2.2) per 100 person-years for infants aged 0–2, 0–5, and 0–11 months, respectively. IRs (95% CIs) of the first all-cause LRTI episode were 10.7 (8.1–14.0), 11.7 (9.6–14.0), and 8.7 (7.5–10.2) per 100 person-years, respectively. IRs varied by country (RSV-LRTI: 0.0–8.3, all-cause LRTI: 0.0–49.6 per 100 person-years for 0- to 11-month-olds). Conclusions RSV-LRTI IRs in infants in this study were relatively low, likely due to reduced viral circulation caused by COVID-19–related nonpharmaceutical interventions. Clinical Trials Registration NCT03614676. [ABSTRACT FROM AUTHOR]