Age Decomposition of Mortality Rates Among Children Younger Than 5 Years in 47 LMICs

Despite a global decline in the mortality rate of children younger than 5 years (the under-5 mortality rate), neonatal deaths continue to present a substantial challenge. The etiology behind deaths varies between the early and late neonatal periods as well as at later ages.

To decompose the under-5 mortality rate in 47 low- and middle-income countries into 8 age intervals, providing a comprehensive understanding of varying vulnerability across age groups.

This cross-sectional study used nationally representative data from 47 Demographic and Health Surveys conducted between 2014 and 2023 in low- and middle-income countries, including 1.4 million live births.

Age in days, weeks, months, or years.

The under-5 mortality rate was decomposed by age based on a life table approach, using true cohort probabilities for the early and late neonatal periods and synthetic cohort probabilities for other age intervals, to obtain deaths per 1000 live births (ie, the cohort entering the life table) for each age interval.

In the pooled sample of 1 448 001 live births, there were 14 576 deaths in the early neonatal period (age 0 to 6 days); 3400 in the late neonatal period (age 7-27 days); 6760 in the early postneonatal period (age 28 days to 5 months); 4912 in the late postneonatal period (age 6-11 months); and 5145, 3990, 2674, and 1640 at ages 1, 2, 3, and 4 years, respectively. The early neonatal mortality rate accounted for 21.3 (95% CI, 20.5-22.1) deaths per 1000 births from a total under-5 mortality rate of 57.7 (95% CI, 56.2-59.3) deaths per 1000 births. The early neonatal mortality rate was significantly higher than mortality at subsequent ages (eg, median [IQR] mortality rates: early neonatal period, 18.8 [14.3-23.2] deaths per 1000 births; late neonatal period, 4.7 [3.1-5.9] deaths per 1000 births) and much higher when considering the average daily mortality rate. The early neonatal mortality rate accounted for the greatest share of under-5 mortality rate in all but 2 countries. In most countries the lowest mortality rates were observed at age 3 or 4 years. The share of deaths occurring in the late postneonatal period and later was greater in countries with greater under-5 mortality rates.

The concentration of mortality in the first week after birth underscores a critical need for enhanced maternal and neonatal health care. Furthermore, early neonatal mortality rates should be routinely reported and included in health targets. In this study, the age of 6 months emerged as an important turning point: high-mortality countries were characterized by a greater concentration of deaths after age 6 months than countries with lower under-5 mortality rate.