COVID-19 PANDEMIC: The Outbreak- How the Virus Got Out

The most extensive travel restrictions to stop an outbreak in human history haven’t been enough. We analyzed the movements of hundreds of millions of people to show why.

CHINA
Bangkok
Hong Kong
Tokyo
Seoul
Taipei
Singapore
Macau
Ho Chi Minh City
Kaohsiung
Osaka
Phnom Penh
JAPAN
SOUTH
KOREA
TAIWAN
THAILAND
VIETNAM
MYANMAR
Dozens
of cases
Nearly a
thousand cases
Wuhan
Wuhan
Enshi
Jingzhou
Xianning
Hubei
Enshi
Beijing
Shenzhen
Urumqi
Lhasa
Chengdu
Kunming
Harbin
Shanghai
Xi’an
Beijing
Shenzhen
Chongqing
Chengdu
Kunming
Shanghai
Xi’an
Guiyang
Wenzhou
Fuzhou
Changsha
Jining
Chongqing
Nanchang
Xinyang
Hefei
Zhengzhou
Xianning
Suizhou
Xiangyang
Huangshi
Yichang
Jingmen
Shiyan
Europe
South Korea
and Japan
North America
Middle East
Wuhan
South Asia
Southeast
Asia
Australia and
New Zealand
South America
Africa
Edmonton
Winnipeg
Montreal
Manchester
Edinburgh
Dublin
Calgary
Toronto
Boston
Berlin
Birmingham
Vancouver
New York
Chicago
Detroit
Dusseldorf
London
Amsterdam
Moscow
Stockholm
Gothenburg
Washington D.C.
Orlando
Seattle
Seoul
Daegu
San Francisco
Atlanta
Busan
Houston
Los Angeles
Paris
Budapest
Jeju
Florence
Milan
Frankfurt
Prague
Madrid
Sapporo
Fukuoka
Osaka
Shizuoka
Hiroshima
Tokyo
Vienna
Athens
Munich
Almaty
Rome
Stuttgart
Barcelona
Okinawa
Nagoya
Algiers
Istanbul
Tehran
Tbilisi
Islamabad
Tel Aviv
Lahore
Kathmandu
Delhi
Mandalay
Honolulu
San Diego
Phoenix
Taipei
Chiang Mai
Chiang Rai
Dhaka
Kaohsiung
Hong Kong
Yangon
Dubai
Karachi
Kolkata
Macau
Mumbai
Bangkok
Luang
Prabang
Hanoi
Bangalore
Chennai
Manila
Da Nang
Vientiane
Cebu
Colombo
Ko Samui
Siem Reap
Nha Trang
Surat
Thani
Phnom Penh
Ho Chi Minh City
Krabi
Cairns
Kota Kinabalu
Phuket
Malé
Sihanoukville
Brisbane
Perth
Penang
Auckland
Wellington
Sydney
Adelaide
Johannesburg
Singapore
Kuala
Lumpur
Langkawi
Jakarta
Surabaya
Denpasar
Christchurch
Melbourne
Nairobi
Casablanca
Brussels
Zurich
Geneva
Bandar Seri Begawan
São Paulo
Buenos Aires
Mexico City
Bishkek
New York
Seattle
Bay
Area
Los
Angeles
New
Orleans
Alaska
Ala.
Ark.
Ariz.
Calif.
Colo.
Conn.
D.C.
Del.
Fla.
Ga.
Hawaii
Iowa
Idaho
Ill.
Ind.
Kan.
Ky.
La.
Mass.
Md.
Maine
Mich.
Minn.
Mo.
Miss.
Mont.
N.C.
N.D.
Neb.
N.H.
N.J.
N.M.
Nev.
N.Y.
Ohio
Okla.
Ore.
Pa.
S.C.
S.D.
Tenn.
Texas
Utah
Va.
Vt.
Wash.
Wis.
W.Va.
Wyo.
P.R.
Deliveryman
Man
Woman
Woman

It seems simple: Stop travel, stop the virus from spreading around the world.

Here’s why that didn’t work.

Many of the first known cases clustered around a seafood market in Wuhan, China, a city of 11 million and a transportation hub.

Four cases grew to dozens by the end of December. Doctors knew only that the sick people had viral pneumonia that did not respond to the usual treatments.

The true size of the outbreak was much larger even then — an invisible network of nearly 1,000 cases, or perhaps several times more.

 

Estimates from Trevor Bedford, University of Washington, and Lauren Gardner, Johns Hopkins University

With each patient infecting two or three others on average, even a perfect response may not have contained the spread.

But Chinese officials did not alert the public to the risks in December. It wasn’t until Dec. 31 that they alerted the World Health Organization and released a statement — and a reassurance.

“The disease is preventable and controllable,” the government said.

The timing of the outbreak could not have been worse. Hundreds of millions of people were about to travel back to their hometowns for the Lunar New Year.

Here’s how people moved around on Jan. 1, according to a Times analysis of data published by Baidu and major telecoms, which tracked the movements of million of cell phones.

 

Travel volume on Jan. 1. Minor routes not shown.

At least 175,000 people left Wuhan just on that day, we found.

 

Travel from Wuhan on Jan. 1

The departures from Wuhan accelerated over the next three weeks. About 7 million people left in January, before travel was restricted.

 

Travel from Wuhan on Jan. 21

Thousands of travelers were infected.

 

Red dots show proportion of infected travelers, based on estimates from Jeffrey Shaman, Columbia University.

By the time Chinese officials acknowledged the risk of human-to-human transmission on Jan. 21, local outbreaks were already seeded in Beijing, Shanghai and other major cities.

 

Cases as of Jan. 21

Travel on Jan. 21

Two days later, the authorities locked down Wuhan, and many cities followed in the next few weeks. Travel across China nearly stopped.

 

Cases as of Jan. 21

Travel on Feb. 4

But local outbreaks were already growing quickly.

 

Cases as of Feb. 4

Travel on Feb. 4

As the outbreak moved across China in early January, international travel continued as normal.

 

Recent air travel, based on first quarter 2019 data from OAG

Thousands of people flew out of Wuhan to cities around the world.

Over 900 people went to New York every month on average, based on recent trends …

… over 2,200 to Sydney …

… and over 15,000 people went to Bangkok, the most popular destination.

That’s where the first known overseas case appeared in mid-January, a 61-year-old woman who traveled from Wuhan to Bangkok despite having a fever, headache and a sore throat.

Other early cases turned up in Tokyo, Singapore, Seoul and Hong Kong. The U.S. confirmed its first case near Seattle.

 

Cases as of Jan. 23

About 85 percent of infected travelers went undetected, researchers believe. But they were still contagious.

 

Infected people, based on estimates by Jeffrey Shaman

It was only at the end of January that Wuhan was placed under a lockdown and airlines started canceling flights. By Jan. 31, when the United States announced it would shut down entry from China for non-Americans, travel out of Wuhan had basically stopped.

It was too late. Outbreaks were already growing in over 30 cities across 26 countries, most seeded by travelers from Wuhan.

 

Cases as of Jan. 31

The virus started spreading locally, moving easily in confined spaces like churches and restaurants, and infecting people who had not traveled to China — the start of a pandemic.

 

Cases as of Feb. 14

By March 1, thousands of cases were reported in Italy, Iran and South Korea. China was no longer the main driver of the outbreak.

 

Cases as of March 1

In fact, as China started systematically testing, tracing and isolating patients, new cases there declined dramatically, showing that it was possible to slow the virus. Similar measures slowed the spread in Singapore, Hong Kong and South Korea.

In the United States, where testing has lagged, President Trump suspended most travel from Europe. “The virus will not have a chance against us,” he said.

 

Cases as of March 11

But by then, the virus had a secure foothold. It continued to spread locally throughout parts of Seattle, New York City and across the country, once again outpacing efforts to stop it.

 

Cases as of March 20

Notes: The cases shown in each world city include those in the broader metropolitan area or region and include patients who were transferred and treated there.

Sources:
Travel patterns across China are based on data published by Baidu, and data from two Chinese telecoms published by Cao et al., “Incorporating Human Movement Data to Improve Epidemiological Estimates for 2019-nCoV.” Both sources tracked the movements of cell phones.

Estimates of the size of the early outbreak in Wuhan are from Trevor Bedford, associate professor, Fred Hutchinson Cancer Research Center and the University of Washington; Bedford, “Phylodynamic estimation of incidence and prevalence of novel coronavirus infections through time”; and Lauren Gardner, associate professor and co-director of the Johns Hopkins Center for Systems Science and Engineering; Gardner et al., “Update January 31: Modeling the Spreading Risk of 2019-nCoV.”

Estimates of the number of infected people who left Wuhan are from Jeffrey Shaman, professor of environmental health sciences at Columbia; and Li et al., “Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus.”

Normal air travel patterns from Wuhan are from 2019 data from OAG. Travel patterns in 2020 are from Cirium.

Case data from Times reporting; local governments and health officials; The Center for Systems Science and Engineering at Johns Hopkins University; National Health Commission of the People’s Republic of China; and the World Health Organization.

Additional sources:

• Elizabeth Halloran, professor of biostatistics at the University of Washington and researcher at the Hutchinson Center;
• Alessandro Vespignani, professor and director of the Network Science Institute at Northeastern University;
• Chinazzi et al., “The effect of travel restrictions on the spread of the 2019 novel coronavirus outbreak”;
• Arthur L. Reingold, professor and division head of epidemiology and biostatistics at the University of California at Berkeley;
• Benjamin F. Maier and Dirk Brockmann, “Effective containment explains sub-exponential growth in confirmed cases of recent COVID-19 outbreak in Mainland China”

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