Preterm birth complications was the leading cause of death among Indian children under the age of five in 2015, followed by pneumonia, intrapartum-related events and diarrhoea, according to two studies published in The Lancet.
Preterm birth complications accounted for 25.5 per cent of the under 5 mortality, followed by pneumonia, a largely preventable but sometimes deadly infectious disease, which accounted for 15.9 per cent of such deaths.
Intrapartum-related events (during labour and after birth) and diarrhoea made for 11.1 per cent and 8.9 per cent of such deaths respectively.
The studies highlighted that India had more deaths among children under five than any other country in 2015, with large disparities in the child mortality rates between richer and poorer states.
Most (57.9 percent) of deaths among Indian children under five in 2015 occurred in the first four weeks of life - the neonatal period, one of them stated.
Infectious illnesses were more often among the top causes of child deaths in poorer and high mortality states.
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Published in The Lancet Global Health, the studies used data from India and elsewhere to estimate the causes of death among children under five years of age between 2000 and 2015.
The researchers at the Johns Hopkins Bloomberg School of Public Health in the US analysed state-level Indian data on the causes of death among children under five for the years 2000-2015.
Uttar Pradesh (84,362) recorded the highest number of preterm birth complications in 2015, followed by Bihar (36,289), Madhya Pradesh (35,503) and Rajasthan (30,402).
Uttar Pradeh (53,681) again topped the list among deaths of children under five due to pneumonia followed by Bihar (25,052), Madhya Pradeesh (21,693) and Rajasthan (14,467).
Intrapartum related events caused the most deaths in Uttar Pradesh (36,685), Bihar (16,280), Madhya Pradesh (10,400) and Andhra Pradesh and Telangana together (7822).
For diarrhoea, the states with the most deaths were Uttar Pradesh (35 381 plus) followed by Bihar (15,966), Madhya Pradesh (12 575+) and Rajasthan (7274+).
The researchers also estimated that two leading bacterial causes of pneumoniaStreptococcus pneumoniae and Haemophilus influenzae type b (Hib)accounted for 69,000 and 16,000 deaths in children under five, respectively, in India in 2015.
These bacteria can also cause life threatening cases of meningitis and other serious infections in children.
The researchers estimated that there was an 81 per cent decline in Hib deaths and 58 per cent decline in pneumococcal deaths between 2000 and 2015.
The sustained use of the Hib-containing pentavalent vaccine helped accelerate the reduction of pneumonia deaths, said Dr Brian Wahl, an assistant scientist in the Department of International Health at the Johns Hopkins Bloomberg School of Public Health and co-lead author of one of the studies.
"The scale-up of pneumococcal conjugate vaccine will help further accelerate the reduction of deaths due to Streptococcus pneumoniae, which is one of the leading single killers of children in India," said Dr Wahl, who works in the International Vaccine Access Center at the Bloomberg School.
The researchers found that India made great progress during the period, reducing annual mortality among children under five from 2.5 million in 2000 to 1.2 million in 2015 -- which was still the highest in the world.
However, among India's states, great disparities remained: The highest mortality rate in Assam was more than seven times that in Goa.
"India can accelerate its reduction of under-five mortality rates by scaling up vaccine coverage and improving childbirth and neonatal care, especially in states where mortality rates remain high," said Li Liu, PhD, assistant professor at the Bloomberg School.
To accelerate India's progress against child mortality, the team recommended more extensive use of childhood vaccines, particularly against pneumonia- and meningitis-causing Streptococcus pneumoniae and Hib.
They also advocated -- especially for higher-mortality regions -- a scaling up of standard care strategies for newborns, including "kangaroo care" in which the baby rests against the mother's skin, thermal care to reduce hypothermia and early initiation of breastfeeding.