The most important number in the world

Vox

29-03-2025

is an editorial director at Vox overseeing the climate, tech, and world teams, and is the editor of Vox's Future Perfect section. He worked at Time magazine for 15 years as a foreign correspondent in Asia, a climate writer, and an international editor, and he wrote a book on existential risk.
I was an English major in college, and my favorite poet was the first-generation Romantic William Wordsworth. For one thing, there's the name, the best example of nominative determinism in the annals of English literature.
But what I most love about Wordsworth is the way he acts as a bridge between the formal, at times stultified style of the poetry that came before him, and the dawn of a new era that venerated individual emotion and experience — both the good and the ill. All that comes together in one of my favorite Wordsworth poems: 'Surprised by Joy'
Love, faithful love, recalled thee to my mind--
But how could I forget thee? Through what power,
Even for the least division of an hour,
Have I been so beguiled as to be blind
To my most grievous loss?
Beneath the archaic language, the 'thees' and so forth, the verse describes a father who is temporarily distracted from his loss by a moment of joy, only to recall with agonizing suddenness that the one person he wishes to share it with — his young child — is gone. The 'surprise' in 'Surprised by Joy' is that it was possible, even for the briefest moment, for the poet not to be consumed by that 'most grievous loss.'
Like most of Wordsworth's poems, 'Surprised by Joy' was drawn from his personal experience — in this case, the loss of his daughter Catherine in 1812, when she was just three years old. Wordsworth and his wife Mary had five children, two of whom died young: Catherine, and their son Thomas, who passed away from measles at age 6, just a half year after Catherine's death.
To lose two young children in less than a calendar year is a grief I cannot fathom. But it was unbearably common at the time. Nearly one in every three children in England in 1800 died before the age of 5. In 1900 in the US, the death rate for children was nearly one in five, as my Vox colleague Anna North wrote recently. Look back over the full course of human history, and it is estimated that nearly one in every two children died before reaching their 15th birthday.
It might be comforting, perhaps, to pretend that the parents of the past weren't as affected with the death of a child, because it was so common. After all, family sizes used to be much larger, in part because of the ubiquity of childhood mortality.
Yet Wordsworth's lines bury that comfort in the graveyard where it belongs. In 2025, in 1812, in 2000 BC, the death of a young child is the worst thing that could happen to any parent.
The most important number in the world
You're probably wondering, 'Where's the good news?' Here it is: The rate of childhood mortality is now far, far lower than it once was. Best of all, it's continuing to drop.
In 1990, 12.8 million children died before the age of 5, but in the years since that number has fallen by more than 60 percent. According to new data released by the UN this week, the number of under-5 deaths fell to a record-low of 4.8 million in 2023.
At Vox's Future Perfect, the section I run, we like to refer to the drastic drop in child mortality as the most important statistic in the world, for several reasons:
If a child can make it to their fifth birthday, it significantly increases their chance of living a full life. Given that life expectancy overall has increased hugely as well , that can mean the difference between a life of a few years and one that extends to 70 years or more. With millions of children alive today who would have been dead just a few decades ago, that adds up to billions of years of additional life.
Child mortality is one of the most important indicators of a country's development. As the chart above shows, rich nations like the UK and the US first made progress in keeping children alive, but more recently poorer nations like India have made tremendous strides. (Child mortality dropped an astounding 81 percent between 1980 and today in India.)
The reduction in child mortality is perhaps the best example of the international community setting a goal and making major progress toward it. In 2000, the UN aimed to reduce child mortality to two-thirds below 1990 levels by 2015. While we didn't quite make it by then, we're almost there now. Global health is a bright spot compared to the struggles in making progress on climate change.
We shouldn't need economic motivations to want to reduce child deaths, but reduced childhood mortality is also associated with better economic performance. Family sizes fall to a more manageable level in poor countries, and more future workers survive to a productive age.
How did we get here — and where are we going?
There is no secret formula to reducing child mortality. Improved prenatal, childbirth, and postnatal care all keep children alive in their vulnerable first months. Better sanitation and nutrition prevent early deaths from waterborne illnesses and malnutrition.
Vaccines have, of course, saved untold millions of children from once common killers like measles, diphtheria and polio. (Let me say this again louder for those in the back row, especially if any of you happen to currently be running the Department of Health and Human Services: VACCINES!)
Despite this tremendous success, 4.8 million children — approximately the population of Phoenix — still die before their fifth birthday, which is exactly 4.8 million too many. The world would have to reduce child mortality by an additional 30 percent or so to meet the new UN goal of essentially ending preventable child deaths 2030.
Unfortunately, we're not on that trajectory. While the number of child deaths is still declining, progress has been slowing down, and that was before the massive cuts in foreign aid in the US and other countries. The highest levels of child mortality today are found in extremely poor sub-Saharan African nations like Chad and Mali where aid will be the difference between life and death.
Here in the US, the turn away from childhood vaccines risks reintroducing long-conquered killers of children. The fact that an unvaccinated child in Texas recently died of the measles — the same disease that took Wordsworth's son Thomas, back when there was no protection from the virus — should horrify all of us.
Whether it is through resurrecting the most effective forms of foreign aid, or reconfirming our trust in vaccines that have saved millions, it is in our power to eventually end preventable child deaths. We can ensure that one day no parent will experience the pain suffered by William Wordsworth and by countless parents before and after him. Such an achievement would be a joy that lasts.
A version of this story originally appeared in the Good News newsletter. Sign up here!
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