Despite a dramatic decline in the number of deaths among children and adolescents worldwide in the past few decades, global progress remains uneven, according to new research.

The study, published Monday in JAMA Pediatrics, found that childhood and adolescent deaths worldwide dropped by nearly half — from 14.2 million in 1990 to just over 7.2 million in 2015.

The most common causes of death reported were preterm birth complications in newborns, lower respiratory tract infections, diarrheal illnesses, congenital anomalies, malaria, neonatal sepsis, meningitis, and HIV and AIDS.

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The greatest number of deaths among children and adolescents occurred in South Asia and sub-Saharan Africa.

An international team of researchers looked at data from 195 countries and territories from 1990 to 2015. They took into account income, education, and fertility to calculate a Sociodemographic Index (SDI) in each country.

The results show that countries with lower SDIs had a greater share of the burden of childhood deaths in 2015 compared with 1990. While there was progress even in less developed countries, inequality increased as more advanced countries pulled further ahead.

The authors conclude that despite advancements medicine and dramatic improvement in child and adolescent health in recent decades, more needs to be done to distribute these benefits to children around the globe.

“If we are going to continue the current pace of improvement in child and adolescent health, we must invest in better data collection, continue to monitor trends in population disease burden, and adapt health systems to meet the ongoing and changing needs of children and adolescents so that all can have a chance to grow up to be healthy,” they write.

In an accompanying editorial, Christopher R. Sudfeld, Sc.D., and Wafaie W. Fawzi, DrPH, of the Harvard T.H. Chan School of Public Health, say paying greater attention to early childhood and adolescent health is “critical.”

“Halving the number of global deaths in children younger than 5 years from 1990 to 2015 was a remarkable achievement; however, we are significantly lagging in reductions of preventable stillbirths and neonatal deaths, particularly in vulnerable populations. Additional financial and intellectual investments in adolescent health are also necessary to promote healthy behaviors and reduce risks that can have lifelong implications for adolescents, their families, and their communities.”