Even drastic interventions to limit the spread of the coronavirus take around 10 days to start to show an effect. The US still hasn’t put those measures into place.

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Note: The data in the charts for Italy and the US was updated through April 12. For the past few days, President Donald Trump has railed against medical advisers who maintain that the nation needs to persist with social distancing — or face a catastrophic death toll from COVID-19, the disease caused by the novel coronavirus.

“WE CANNOT LET THE CURE BE WORSE THAN THE PROBLEM ITSELF,” he tweeted on March 22, referring to the unprecedented economic downturn triggered by the response to the outbreak. Two days later, Trump said he wanted to put the nation back to work by Easter, which falls on April 12. “I would love to have the country opened up and just raring to go by Easter,” he told a Fox News town hall. “You'll have packed churches all over our country. I think it would be a beautiful time." Looking at the seemingly inexorable rise in US cases and deaths, it’s easy to conclude that interventions to limit the spread of the virus aren’t working. But the dynamics of viral outbreaks mean that the economic pain of these measures will be felt before their intended benefits start to visibly kick in. “Any interventions we make today will not show up in our data for 1-2 weeks,” Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security in Baltimore, warned on Twitter on March 18. “The time it takes to show symptoms after being infected is about 5 days, and then it takes a few more days to get diagnosed and counted. For a while it will feel like nothing is working but it takes time.” “Most infectious disease experts are concerned about right now being too soon — far too soon — to end social distancing measures here in the US,” computational epidemiologist Maia Majumder told BuzzFeed News. “The thing about public health interventions is that it usually takes some time before we actually see their effects at the population level.” What’s more, epidemiologists say that drastic measures — including social distancing, business closures, widespread testing, and strict isolation orders for positive cases — will need to be kept in place for weeks to months to prevent the virus from surging back. The experience of two countries that managed to turn back the tide of COVID-19 — China and South Korea — bears this out.

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This chart of new cases diagnosed per day is known as an “epidemic curve.” As a disease outbreak comes under control, the number of new cases should peak and then gradually decline. COVID-19 first emerged late last year in the Chinese city of Wuhan. On Jan. 23, China placed Wuhan and neighboring cities, upwards of 50 million people, under a strict quarantine — including suspension of all public transportation and widespread road closures. As the chart shows, the peak in daily new cases came 10 days later, after which the curve turned downward. (There was also a big spike on Feb. 13, not shown here, which was due to a change in the way cases were diagnosed rather than a real surge in new cases.)

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South Korea is the standout example of a country that controlled its COVID-19 outbreak before things got out of hand. It did that by quickly ramping up widespread diagnostic testing, and then tracking and isolating people who had been in contact with known cases. As a result, it didn’t have to resort to a drastic lockdown of its economy. As the chart shows, the peak of South Korea’s epidemic came on Feb. 29, 10 days after the number of tests performed passed 10,000. By the time the epidemic was at its peak, almost 100,000 diagnostic tests had been run, and the figure has since passed 350,000.

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Italy has been hit especially hard by the coronavirus. By the time the nation realized the mess it was in, it was too late to copy South Korea’s approach. After starting with a piecemeal approach of isolating individual cities and regions, on March 9 the entire nation was placed on lockdown, restricting travel to work and emergencies. Since then, the measures have been tightened further and enforced by the military, with parks and all but essential manufacturing shut down by March 21. It’s too early to be sure that these policies are having their desired effect, but the chart suggests that new cases may have peaked on March 21, 12 days after the initial national lockdown. Each of these countries have persisted with the policies that seemed to halt the march of COVID-19, and epidemiologists warn that the virus is likely to surge back if nations let down their guard too early. “[W]e predict that transmission will quickly rebound if interventions are relaxed,” wrote a team at Imperial College London in an epidemiological modeling study released March 16 that shocked the British government into its own lockdown measures.



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