Severe RSV hits youngest infants earliest
In low- and middle-income countries, the most severe respiratory syncytial virus illness clusters in the first weeks of life.
*Systematic review and meta-analysis of observational studies; Level 1a (OCEBM).

Citation

Mahmud S, van Zandvoort K, Guo L, et al. Age distribution of respiratory syncytial virus disease in children younger than 5 years in low-income and middle-income countries: a systematic review and meta-analysis. Lancet Child Adolesc Health. 2026;10:245–254.

Background

Global guidance supports passive protection against respiratory syncytial virus (RSV) in early infancy, but choosing the best timing requires detailed age patterns across mild to severe outcomes.

Patients

Children younger than 5 years in low- and middle-income countries; pre-pandemic data (2010–2019). Included datasets required at least 30 laboratory-confirmed RSV cases for one outcome in one country (a few death datasets had 20–29 in sensitivity analyses).

Intervention

Not applicable (age-distribution modeling of observed RSV outcomes).

Control

Not applicable.

Outcome

Age distributions for community cases, outpatient visits, emergency visits, hospital ward admissions, intensive care unit admissions, and deaths (in and out of facilities).

Follow-up Period

Data collected during 2010–2019 (pre-COVID-19 decade).

Results

160 datasets from 43 countries contributed 131,124 RSV-positive counts. More severe outcomes occurred at younger ages.
RSV outcome Peak age (weeks) Share in infants <6 months Share in infants <8 weeks
Non-facility deaths 3 57% —
Facility deaths 4 57% 23%
Intensive care unit admissions 7 60% 20%
Hospital ward admissions 17 41% —
Emergency visits 10 40% —
Outpatient visits 28 19% —
Community cases 22 26% —

Limitations

RSV test positivity does not prove RSV caused the illness or death. Very few datasets informed death estimates, especially outside facilities. The modeling assumed no cases on day 0 of life and may miss neonatal, sepsis-like presentations. Individual risk factors (eg, prematurity) were not available.

Funding

World Health Organization (grant from the Gates Foundation).

Clinical Application

Plan RSV protection to start at birth or very early infancy; many intensive care admissions and deaths occur before 8 weeks, especially in low- and middle-income countries.