A Chinese worker checks the temperature of a customer as he wears a protective suit and mask at a supermarket on February 11, 2020 in Beijing, China. The number of cases of a deadly new coronavirus rose to more than 42000 in mainland China Tuesday, days after the World Health Organization (WHO) declared the outbreak a global public health emergency. China continued to lock down the city of Wuhan in an effort to contain the spread of the pneumonia-like disease which medicals experts have confirmed can be passed from human to human. In an unprecedented move, Chinese authorities have put travel restrictions on the city which is the epicentre of the virus and municipalities in other parts of the country affecting tens of millions of people. The number of those who have died from the virus in China climbed to over 1000 on Tuesday, mostly in Hubei province, and cases have been reported in other countries including the United States, Canada, Australia, Japan, South Korea, India, the United Kingdom, Germany, France and several others. The World Health Organization has warned all governments to be on alert and screening has been stepped up at airports around the world. Some countries, including the United States, have put restrictions on Chinese travellers entering and advised their citizens against travel to China. (Photo by Kevin Frayer/Getty Images) A Chinese worker checks the temperature of a customer as he wears a protective suit and mask at a supermarket on February 11, 2020, in Beijing, China. The number of cases of a deadly new coronavirus rose to more than 42,000 in mainland China Tuesday, Feb. 18, days after the World Health Organization (WHO) declared the outbreak a global public health emergency. (Photo by Kevin Frayer/Getty Images)

(Bloomberg) — It’s already spread wider than SARS in 2003. It may not sweep the globe as swine flu did in 2009, but is more dangerous. It doesn’t kill at anywhere near the terrifying pace of Ebola in 2014, but it can be passed through the air.

Even as the number of new coronavirus cases in China appears to ebb, experts say they’re preparing for a future with a disease that past pandemics have only hinted at.

China’s lockdown of Hubei province, where the outbreak began, gave the world several weeks to throw up its defenses, global health officials said Tuesday, February 18, 2020. But it hasn’t stopped the virus, with new cases popping up around the globe, potentially seeding a pandemic to come.

“Every virus is different,” said University of Michigan medical historian Howard Markel, who has studied influenza epidemics. “If anything the study of past epidemics has taught me is that anyone who predicts the future based on that is either a fool or lying because we don’t know.”

Epidemics are usually defined as outbreaks of disease that are mostly confined to a particular region or country. When they spread and create multiple, ongoing outbreaks in different regions or countries, they can be considered pandemic. Health experts are watching closely to see if new, sustained outbreaks of the virus take hold outside China.

The virus has brought together elements that scare public health experts as well as average citizens. In less than three months, it’s infected tens of thousands of people. Humans have never faced it, leaving their immune systems vulnerable. And there are no vaccines to prevent 2019-nCoV, as the virus is called, or to treat the disease it causes, Covid-2019.

Four Scenarios for the Coronavirus Outbreak (Photo: Bloomberg)

One certainty is that new cases will continue to emerge. On Saturday, an American passenger from a cruise ship that docked in Cambodia tested positive for the virus. It raised new worries that disembarked passengers from the boat, previously thought to be virus-free, would seed new pockets of disease.

The U.S. Centers for Disease Control and Prevention said last week that it will begin screening patients with flu symptoms for 2019-nCoV in five major U.S. cities. The effort is meant to detect whether the virus has slipped into the U.S. despite robust travel screening and quarantines that have caught the less-than-20 American cases identified so far.

The aspects the new coronavirus does share with other outbreaks are mostly human failures, not biological advantages.

In 1892, authorities in Hamburg, Germany — worried about impact cholera would have on their thriving port — initially kept quiet about some cases, allowing the disease to spread, said Markel. More than 8,000 eventually died in the city. And the disease soon arrived in New York. In Wuhan, local Chinese officials have been accused of minimizing the threat from the virus in the early weeks when it could have been more easily stopped.

Willingness to endure economic disruption is another factor, said Markel. Epidemics are always enormously costly. Stopping trade and movement can slow a disease’s spread, but grind economies to a halt.

In a study published this month, the Chinese Center for Disease Control and Prevention warned that even with new infections in decline, they could rise again as the economy restarts, after an extension of the national Lunar New Year holiday and shutdowns of workplaces and public gathering spaces.

“Huge numbers of people will soon be returning to work and school,” a group of researchers at the Chinese agency wrote in their analysis. “We need to prepare for a possible rebound of the Covid-19 epidemic in the coming weeks.”

On the virus biology side, researchers still don’t know many basic parameters. One of the most crucial unknowns is whether the virus can spread when people aren’t showing symptoms. If a large fraction of people can catch and transmit the virus before becoming seriously ill, the odds of halting it with existing measures plummet, according to computer simulations run by the London School of Hygiene & Tropical Medicine.

“This virus has a firm foothold,” said Steven Riley, professor of infectious disease dynamics at Imperial College London’s MRC Centre for Global Infectious Disease Analysis. “There are many more people with it than there ever was with SARS. We don’t want this virus to become an established human pathogen. If it takes off in other parts of the world and remains a relatively severe virus, it would become a new kind of thing.”

The world should get a better view of how significant the outbreak will be in the next few weeks, as additional surveillance gives clearer insights into the virus’s spread by mid-March, said Michael Osterholm, an expert on infectious diseases at the University of Minnesota.

“We are just getting started,” he said. “If this spreads around the world, this will be just south of the 1918 pandemic,” he said, referring to the pandemic flu that killed millions a century ago. “The next three weeks are going to be critical.”

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