The UNICEF said 1.2 million children under five could die in just six months on top of the 2.5 million children who already die in the 118 countries included in the study.
The estimate is based on an analysis of the indirect effects of the pandemic on maternal and child mortality in 118 low- and middle-income countries.
The analysis was conducted by Johns Hopkins Bloomberg School of Public Health modeling three scenarios depending on the reductions in lifesaving interventions.
It was published in The Lancet Global Health journal on Tuesday.
In the most optimistic scenario, where the pandemic leads to a 15% reduction in health services, under-five child deaths could increase by 9.8% (an estimated 1,400 a day) and maternal deaths could increase by 8.3% per month.
In the worst-case scenario, where health services are reduced by 45%, under-five child deaths could increase by 44.7% while maternal deaths could increase by 38.6% per month.
The study's authors said, "Our estimates are based on tentative assumptions and represent a wide range of outcomes."
They added, "Nonetheless, they show that, if routine healthcare is disrupted and access to food is decreased (as a result of unavoidable shocks, health system collapse, or intentional choices made in responding to the pandemic), the increase in child and maternal deaths will be devastating."
UNICEF's UK's executive director Sacha Deshmukh said, "This pandemic is having far-reaching consequences for all of us, but it is undoubtedly the biggest and most urgent global crisis children have faced since the second world war."
Deshmukh added, "Children's lives are being upended across the globe—their support systems ripped away, their borders closed, their educations lost, their food supply cut off."
According to the UNICEF, the 10 countries estimated to have the greatest additional number of child deaths in the worst-case scenario include Bangladesh, Brazil, the Democratic Republic of the Congo, Ethiopia, India, Indonesia, Nigeria, Pakistan, Uganda and the United Republic of Tanzania.
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