Globally, the single biggest killer of young children is complications from being born too early. Preterm birth, along with other newborn complications, infectious diseases like pneumonia and diarrhea, and malaria account for the vast majority of deaths in children under five. Nearly half of all those deaths, 47%, happen in the first 28 days of life.
The Newborn Period Is the Deadliest
The first four weeks after birth are by far the most dangerous stretch of childhood. In 2022, 47% of all deaths in children under five occurred during this neonatal window. The leading killers during this period are premature birth, birth complications (such as oxygen deprivation during delivery), newborn infections, and congenital anomalies. Together, these four causes account for nearly 4 in every 10 deaths among all children under five, not just newborns.
Many of these deaths cluster in the first hours and days. Babies born before 37 weeks of pregnancy often have underdeveloped lungs, difficulty regulating body temperature, and higher vulnerability to infection. In wealthier countries, neonatal intensive care units can manage most of these risks. In low-income settings, even basic interventions like clean delivery environments, immediate skin-to-skin contact, and early breastfeeding support are not always available.
Infectious Diseases After the Newborn Period
Once children survive the first month, infectious diseases become the primary threat. Pneumonia, diarrheal diseases, and malaria are the leading killers of children between one month and five years of age. These are not exotic or untreatable conditions. Pneumonia can often be managed with antibiotics, diarrhea with oral rehydration salts, and malaria with widely available treatments. The deaths happen where access to these basic tools is limited.
Vaccination also plays a major role. Pneumonia and diarrheal diseases are the two biggest vaccine-preventable killers of children. Vaccines against rotavirus, pneumococcal bacteria, and measles have dramatically reduced child deaths in countries with strong immunization programs, but coverage gaps in parts of sub-Saharan Africa and South Asia leave millions of children unprotected.
Malnutrition Underlies Nearly Half of Deaths
Malnutrition rarely appears on a death certificate as the official cause, but it is a driving factor behind an enormous share of child mortality. The WHO has estimated that undernutrition contributes to roughly 45% of all deaths in children under five. A 2024 study published in BMJ Global Health, using detailed postmortem data from seven low- and middle-income countries, found malnutrition was a causal or significant factor in about 40% of under-five deaths, often in combination with infectious diseases.
What this means in practice: a malnourished child who contracts pneumonia or diarrhea is far more likely to die than a well-nourished child with the same infection. Their immune system is weaker, their body has fewer reserves, and they deteriorate faster. Addressing malnutrition is not a separate issue from fighting infectious disease. They are deeply intertwined.
How Causes Shift as Children Get Older
Once children pass their fifth birthday, the picture changes dramatically. Infectious diseases drop down the list, and injuries move to the top. In the United States, 2023 mortality data from the CDC shows accidents (unintentional injuries) are the leading cause of death for every age group from 1 through 19.
For children ages 1 to 4, the top three causes are accidents, birth defects, and homicide. For ages 5 to 9, they shift to accidents, cancer, and birth defects. By ages 10 to 14, the list is accidents, suicide, and cancer. And for adolescents aged 15 to 19, the top three are accidents, homicide, and suicide. The U.S. recorded 12,777 deaths among 15-to-19-year-olds in 2023, a rate of 57.9 per 100,000.
This pattern reflects a broader reality: in high-income countries, medical advances have largely eliminated infectious disease as a major cause of child death. What remains are injuries (many involving cars, drowning, or firearms), violence, mental health crises, and cancers that don’t yet have reliable prevention strategies.
Why Geography Matters So Much
Where a child is born is one of the strongest predictors of whether they will survive to age five. Sub-Saharan Africa and South Asia bear a disproportionate share of global child deaths. A child born in sub-Saharan Africa faces risks from malaria, pneumonia, diarrhea, and malnutrition that have been largely eliminated in wealthier regions. The gap is not mainly about unknown diseases or unsolvable problems. It is about access to clean water, basic vaccines, trained birth attendants, and nutrition support.
In high-income countries, neonatal conditions and congenital anomalies make up a much larger proportion of child deaths, because the infectious disease deaths that would have occurred in a lower-resource setting have already been prevented. This doesn’t mean fewer children die from preterm birth in wealthier countries in absolute terms. It means the other causes have been reduced so significantly that birth complications represent a larger share of what remains.
The Global Picture in Summary
The causes of child death follow a clear pattern shaped by age and geography. In the first month of life, prematurity and birth complications dominate everywhere. From one month to five years, infectious diseases, amplified by malnutrition, are the primary killers in low-income settings. After age five, injuries and violence take over, particularly in higher-income countries where infectious disease has been controlled. Across all of these categories, the majority of deaths are preventable with interventions that already exist. The challenge is delivering them to the children who need them most.