In much of the developed world, the coronavirus curve is slowly flattening, but this obscures a tragic reality — the second phase of the crisis has begun as the novel virus spreads to the developing world. Ten of the top 12 countries with the largest number of new confirmed infections are now from the ranks of emerging economies, led by Brazil, Russia, India, Peru and Chile. The resulting devastation would likely reverse years, if not decades, of economic progress.

For a while, it appeared that the developing world was being spared the worst of the pandemic. As of April 30, with 84 percent of the world’s population, low-income and middle-income countries were home to just 14 percent of the world’s known covid-19 deaths, according to a Brookings Institution report. This can be explained in part by a lack of testing and a failure to attribute deaths to covid-19.

But there may be other factors. Nursing homes, which have accounted for a large share of deaths in wealthy countries, are uncommon in the developing world, so the elderly are not clustered together. Heat may have some effect in reducing the spread of the virus. Some medical experts privately speculate that the populations in these countries have stronger immune systems because they have been exposed to many more diseases over their lifetimes.

There is another possibility. The developing world was spared the disease in the early months because it was less connected, by travel and trade, to the initial hot spots (China and Europe). In the past few weeks, however, the coronavirus has moved slowly but steadily across South Asia and Latin America. Brazil now has about 1,000 recorded deaths a day — and cases are rising exponentially. Africa has not had a large spike in confirmed cases — so far — but anecdotal evidence suggests the disease is spreading there as well. The Wall Street Journal reports that in the northern Nigerian city of Kano, gravediggers are running out of space and have resorted to burying corpses between existing graves or putting multiple bodies in a single grave.

If the curves in these countries do not start flattening, the damage would be worse than anything we have seen in the West. The population density and sanitary conditions make the rapid spread of the coronavirus seem inevitable. In India, a fifth of all known cases come from Mumbai, where one slum, Dharavi, houses about 1 million people and has a population density that is nearly 30 times that of New York City. Africa’s largest city, Lagos, has had relatively few infections so far. Yet the fact that two-thirds of its inhabitants live in slums, many taking crowded buses to work, means it is likely only a matter of time before the numbers rise. Hospital facilities in lower-income countries are sparse. In Bangladesh, there are eight hospital beds for every 10,000 people, a quarter as much as in the United States and an eighth as much as in the European Union. There are fewer than 2,000 ventilators across 41 African countries, compared with 170,000 in the United States.

In many of these countries, large segments of the population make just enough each day to feed themselves and their families. So governments face a deadly dilemma: If you shut down the economy, people could starve. If you keep it open, the virus will spread.

And then there is phase three of the pandemic, the debt crisis, which will hit the developing world very hard. In the United States, Europe, Japan and China, the economic damage is brutal but will be ameliorated by massive government spending. These countries, the United States above all, can borrow trillions at low interest rates with relative ease. That’s not the case for poor countries that are already deeply indebted. They have to take out loans in dollars, which they must pay back in their own (rapidly depreciating) currencies. Down the line, they face the real prospect of hyperinflation or default.

Over the past few decades, as global trade accelerated, the developing world grew faster than rich countries, and standards of living rose accordingly. Even after the global financial crisis, developing countries recovered faster than rich ones did. They were less exposed to complex financial products and weathered the downturn relatively well.

The result has been one of the great “good news” stories of our times — a massive reduction in extreme poverty. From 1990 to 2010, the share of humanity living on less than $1.25 a day halved — twice as fast as the previous halving. This U.N. Millennium Development Goal was achieved five years ahead of schedule.

Now the work of decades is being undone in months. Various studies estimate that somewhere between 100 million and 400 million people will be pushed back into extreme poverty. In this most crucial measure of human progress, we are moving backwards — and fast.

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