(Bloomberg) — The new coronavirus has now infected more than 1 million people across the world, a milestone reached just four months after it first surfaced in the Chinese city of Wuhan. More than 53,000 have died and 211,000 recovered in what has become the biggest global public health crisis of our time.

When the virus was first discovered, doctors likened it to Severe Acute Respiratory Syndrome, or SARS, the illness that sickened 8,000 people mostly in Asia in 2003. Highly contagious, and appearing with little or no symptoms in some cases, Covid-19 has rapidly eclipsed all recent outbreaks in scale and size. Fewer than 20 countries in the world appear to be free of infection.

With some virus carriers presenting few outward signs of illness, and many countries unable or unwilling to conduct wider testing, the true number of global infections is likely higher — some say far higher — than 1 million.

The U.S. now has the most cases officially recorded globally with more than 245,000, according to Johns Hopkins University, which draws on a combination of data sources — from governments to the World Health Organization and local media — to feed its tallies. Next is Italy, with just over 115,000, the JHU data show. Italy has the highest death toll with almost 14,000 virus fatalities, followed by Spain.

With world travel paralyzed and millions of people under some form of lockdown as a result of government efforts to contain the spread, the health crisis has also become an economic one: The global economy is expected to shrink 2% in the first half of 2020. Business activity has ground to a halt in many sectors, with predictions the U.S. jobless rate could reach 30% in the second quarter.

Here’s how we got here

The Pathogen Emerges

Wuhan’s first known virus patient begins developing symptoms on Dec. 1, according to a paper published Jan. 24 in The Lancet medical journal. On Dec. 16, doctors at the Central Hospital of Wuhan send samples from another patient with a persistent fever for lab testing. Those results show a SARS-like virus and on Dec. 30 Ai Fen, the head of the hospital’s ER department, posts a picture of a lab report on Chinese social media, which is re-posted and circulated by several other doctors. They’re reprimanded by local police for “spreading rumors.”

At the end of December, the virus first appears in China’s tightly controlled state media, with reports government officials are probing dozens of cases of a mystery pneumonia in Wuhan. They don’t elaborate further. This is the first time that many within China and the outside world learn about the virus’ existence. By Jan. 3, Singapore, Hong Kong and Taiwan — Asian cities hit hard by the SARS pandemic — institute fever screenings at airports for arrivals from Wuhan, a key transport and manufacturing hub for central China.

The Virus Spreads Beyond Wuhan

On Jan. 11, a team of scientists in Shanghai sequences the complete genome of the virus and publishes it on virological.org, an online discussion forum for epidemiologists. This gives researchers around the world a way to identify the virus in patients and infections are quickly found outside of Wuhan. Thailand confirms its first case on Jan. 13 and three days later one appears in Japan. Cases are reported in Beijing and the southern Guangdong province around Jan. 20, the same day Chinese infectious diseases expert Zhong Nanshan confirms on state television that the virus is spreading between humans.

Things escalate quickly from this point and — with questions being asked about delays in identifying and tackling the outbreak — China’s government starts ordering measures to control the disease’s spread. On Jan. 23, a day before the country’s week-long Lunar New Year holiday, Wuhan is placed under lockdown, with transport halted and restrictions on who can go in and out. The quarantine is expanded quickly to cities surrounding Wuhan and ultimately all of Hubei province, effectively sealing off 60 million people.