Liu Zheng Zheng of the Harvard Business Review China, based in Beijing, contributed to this report

Judging by the forums and private Facebook groups we follow, the most terrifying feature of the Wuhan coronavirus outbreak so far has been the Chinese government’s aggressive response — whole cities and tens of millions on sudden lockdown in their homes, public gatherings banned, internal travel by road cut off with roadblocks.

Why would China take such disruptive and expensive measures to stop the spread of a virus with well under a hundred deaths and a few thousand infections (per the official count)? It doesn’t add up, and the internet has noticed, giving rise to the theory that Chinese are trying to cover up how catastrophically deadly this outbreak really is.

More: Wuhan coronavirus basics and list of updates as we get them

But newly published migration data suggests a far less terrifying logic behind China’s aggressive response: it seems an astonishing five million people bugged out from Wuhan in the days before intercity travel was banned. Some portion of that was due to planned holiday travel, but it’s clear many people left (or left earlier than planned) due to the virus news.

Our Chinese reporter in Beijing explains it this way:

SARS is still fresh in the minds of many Chinese.

Modern Chinese people are already wary of weird food sources as a possible epidemic spark — in this case, it looks like a mix of bat and snake at the local Wuhan food market is to blame.

There’s a degree of mistrust towards the government, so people expect party leaders to downplay legitimate concerns.

Local people were glued to their phones for instant updates very early in this process.

Every social media post that could even seem related, such as a person collapsing at a hospital, instantly spreads.

That combination of predisposed fear, viral media, and modern on-demand transportation networks meant millions of people “bugged out” of Wuhan very quickly.

So the governments only way to contain the spread was to use fast and heavy lockdowns.

But even with such a heavy response, it was too late, and the virus left Wuhan.

More: Read her personal account of what things have been like on the ground, including video examples of what’s spreading through local social media and causing fear. Here’s one example:

This level of sudden, coordinated action across a population of this size in response to breaking news was unthinkable in the days before social media.

But it’s likely now the new normal in societies as connected as China. That new reality makes China’s “shock and awe” response look less like a desperate measure to stop Black Death 2.0 and more like a logical effort to arrest a set of social-media-driven, “flash mob”-style mass migrations before centrally planned containment measures could be put in place.

Wuhan’s population has dispersed across China, carrying the epidemic with it

While initial reports indicated that over a hundred thousand people left Wuhan by rail in the single day before the quarantine, the Times has now reported that including the entire leadup and all travel modes, the true figure was closer to five million people — about 45% of the population of Wuhan.

With so many Wuhan citizens spread to every part of the country, the move to lock down public spaces across the country as a whole makes a certain amount of sense; any measure intended to be effective at arresting the epidemic’s exponential spread would have to be carried out nationwide to be effective.

In addition, this explains the intercity travel ban being put on Wuhan despite the “cat [being] out of the bag”: if a precedent were established that affected cities would empty entirely, as Wuhan may have done, the migrations may have become even more destabilizing as active propagation of the virus began to hit other major cities.

Restrictions are already easing, and that’s a good thing

There’s evidence that some of the harshest restrictions may already be easing somewhat, now that their purpose has been served. In Wuhan itself, reports suggest that the ban on private road travel has been reduced to a strong suggestion, allowing shut-in Wuhan residents to take critical trips to gather supplies or seek medical care.

In general, easing the more dramatic restrictions and leaving in place only those with the most demonstrated power to stop the spread is a good idea, as China settles in for what will likely be a long epidemic even if measures prove as effective as hoped.

The SARS epidemic, for example, took months to resolve even after effective measures were put in place. By the time already-in-motion measures become effective, the 2019-nCoV outbreak will likely be larger than the SARS outbreak.

In addition, the revelation of the size of the initial migration gives some insight into the trend in case locations over the last few days. Until January 23, over 80% of 2019-nCoV confirmed cases were in Hubei province — while in recent days case numbers in cities around China have exploded, with latest tallies showing about as many cases outside Hubei as inside it, with a dozen Chinese cities reporting over 40 cases and two (Guangdong and Zhejiang) showing over a hundred.

But in the context of this new migration information, this dramatic growth in the number of new cases is far less worrying than it would be otherwise. Rather than showing an explosion of local transmission in cities across China, it suggests the possibility that about half the cases originating in Hubei are first showing up elsewhere in China (if the out-migration from Hubei is about half, the same as Wuhan) because people are being diagnosed and counted where they bugged out to and not where they caught the virus.

Whether exponential propagation of the epidemic begins in cities across China despite recent precautions will become clearer in coming days.

The nightmare scenario is now much less feasible

The Wuhan migration numbers provide powerful evidence against one of the scariest scenarios we encountered in our analysis of the academic models of this outbreak’s spread. Specifically, the paper from Jonathan Read, whose predictions were amplified in viral Twitter threads because they were by far the most pessimistic among all the academic epidemiology modeling studies, was based on a diffusion model assuming business-as-usual travel throughout China and the world, and estimated high case numbers and rates of growth in Wuhan in order to explain the frequency of cases emerging elsewhere in China.

Since this diffusion was largely the result of a massive exodus from Wuhan, with travel numbers far above normal, the worse scenarios in the Read paper (including over 250,000 cases of the virus in Hubei alone by February 4) are less likely in light of this new news.

However, the generally higher frequency of travel and the confirmation of asymptomatic transmission both suggest that countries around the world may face even more in-bound infected travelers than the Read paper’s results suggested.

Ultimately, the broader conceptual framework for understanding the outbreak that we laid out on Friday remains intact today: growing case numbers and geographic diffusion mean little by themselves, and the big answers will still take more time to emerge.

Whether China’s travel restrictions and lockdowns are effective at arresting the epidemic’s growth, and whether countries around the world can prevent exponential propagation from arising on their shores, are questions that will take more time to answer. So, by all means keep watching Johns Hopkins University’s excellent coronavirus tracking portal, but continue to stay calm, even as the tone of press coverage grows a bit grimmer.