In Hollywood, movie sequels are often weaker than the originals. For viruses, that logic does not always apply. The virus now named the “severe acute respiratory syndrome coronavirus 2” by the International Committee on Taxonomy of Viruses will have an impact that far exceeds the death toll and economic damage caused by the original SARS.

In late January and early February 2020, China embarked on the most drastic social-distancing measures ever seen, confining hundreds of millions of people to their homes. This approach has been successful in reducing the transmission of the “SARS 2” coronavirus to the extent that daily case numbers have declined throughout China in February.

Outside of China, however, such sweeping social controls will not be possible. The virus is spreading. As of this writing, nearly 30 countries worldwide have reported cases, and local transmission has been reported in new areas almost every day. A brief window of time remains for health authorities around the world to consider what measures they can take to reduce the transmission of the virus and slow its spread—once they acknowledge that containment efforts are futile.


On February 21, 2003, a doctor from Guangzhou, China, traveled to Hong Kong for a family wedding, despite feeling ill. The doctor and his wife checked into room 911 of the Metropole Hotel in the bustling Mong Kok district. By the next morning, the doctor’s symptoms had worsened. He was admitted to a hospital and warned the staff there to put him in strict isolation. He had been treating SARS patients back in Guangzhou.

Twenty-three other Metropole guests developed SARS, transporting the infection to Canada, Ireland, Singapore, Taiwan, the United States, and Vietnam. A global outbreak began that would last almost six more months and ultimately infect more than 8,000 people worldwide, killing almost 800.

Some 17 years later, people around the world face the threat of a new coronavirus pandemic, again originating in China. The novel SARS 2 coronavirus was first identified, in December 2019, in a cluster of pneumonia patients in the city of Wuhan in central China. These cases were initially thought to have originated in a market where wild animals were sold for meat. In fact, community transmission had been occurring since early December, if not earlier. By the time Chinese authorities announced, on January 9, that a new virus had been detected, infections had already spread beyond Wuhan. A Chinese tourist who arrived in Bangkok, Thailand, on January 8, tested positive for the virus on January 13.

Current approaches to containing the infection may not be enough.

By the end of January, 106 infections had been reported in 19 countries, and by February 22, the number had increased to more than 1,400 cases in 28 countries outside of China. Travel reductions have delayed but have not prevented the virus from spreading around the world. Current approaches to containing the infection focus on preventing transmission by identifying and isolating infected people and quarantining their close contacts. But such measures may not be enough.

Effective isolation and quarantine did succeed in containing SARS in 2003 in all the countries it affected. But two key features of the infection made that possible. First, SARS almost always caused serious respiratory symptoms that required hospitalization. Second, SARS patients were not particularly infectious when their symptoms first appeared, but they became more infectious as their illness progressed.

In contrast, the SARS 2 coronavirus often causes mild symptoms, and infectiousness is highest around the time of the illness’s onset. Experts also think that the infection can be passed on before symptoms appear. For these reasons, many infected people will not be identified before they have spread the infection onward, and many will never receive the laboratory test that could confirm they have been infected.


China has limited the transmission of SARS 2 by enforcing extreme social-distancing measures that are probably not possible anywhere else in the world. Major cities in China were ghost towns in early February, with residents required to stay inside as much as possible. In some cities, residents were allowed out of their homes only twice per week to buy groceries. Some municipalities required residents to wear facemasks when they went outside. Schools and workplaces remained closed long after the usual week-long Lunar New Year holiday.

The Chinese government loosened restrictions on movement in mid-February when it introduced a smartphone app to indicate each person’s status: green for people who can leave their homes, yellow for people who need to quarantine themselves at home for seven days, and red for those who need to quarantine themselves at home for 14 days. The app tracks people’s movements and feeds information back into a database of known risk factors. Having contact with people known to be infected or traveling to affected areas changes a person’s status from green to yellow or red. Only those with a status of green are allowed to enter businesses or to use public transportation or public facilities. The restrictions are strictly enforced by local officials and neighborhood committees.

Similar constraints on people’s movements are unlikely to be considered in most other countries, where citizens may be unwilling to accept government monitoring and control over their movements and behavior. Even if people outside of China reduced their social contacts out of fear of infection, such voluntary efforts might not be enough to prevent large outbreaks. Short of cutting off entire populations from the outside world, as some Pacific islands did during the 1918–19 influenza pandemic, preventing an outbreak is almost impossible. So what can be done?

China's coronavirus app
Health codes on China’s coronavirus app

Many countries have already taken measures to delay the importation of infections by reducing the number of travelers arriving from China and other affected countries. Scientists have estimated that screening inbound travelers will identify around one-third of those infected but will miss the other two-thirds. As a consequence, silent transmission has likely already begun in many countries, including the United States.

The priority, then, must be reducing community transmission. There are two ways to do this. The first involves isolating those with laboratory-confirmed cases in special hospital rooms with careful infection control and then identifying their recent close contacts and placing those people under quarantine. If those contacts subsequently show symptoms of infection, quarantine should prevent them from transmitting the virus onward. Such an approach was effective for SARS in 2003 and can be effective for other infections in which the disease is almost always severe (think of the Ebola virus). Containment has largely been the protocol for SARS 2. But isolation, contact tracing, and quarantine will quickly become infeasible in this case, because most SARS 2 infections are mild, and hospitals will run out of space to isolate these mild cases. Contact tracing is labor-intensive. Moreover, the quarantine period has been set at 14 days, which is a long time to hold people who are well, and requires considerable resources. Home quarantine is an option, but it can be difficult to enforce.

The alternative—social distancing—is to reduce contact among people across the community as a whole. During the 1918–19 influenza pandemic, some U.S. cities canceled mass gatherings, closed schools, and prohibited gatherings in confined spaces such as sports stadiums, houses of worship, concert halls, and the like. Businesses found ways to operate with reduced workforces, and nearly everyone used cloth masks or other face coverings. Governments may adopt many of these measures again in 2020 but with potentially serious social and economic consequences. Nonetheless, the interventions may be essential to save lives, particularly if a surge in infections threatens to overwhelm health-care services.


A brief window still remains within which to prepare for what will shortly be recognized as a global pandemic. In the United States, silent transmission is likely happening already, with slow but steady increases in infections supplemented now by infected travelers from affected parts of the world other than China. Once testing begins in earnest in hospitals across the United States, SARS 2 infections will likely be identified in patients having no link to China or other affected areas and no known source of infection.

Italian health authorities have just become aware that infections have likely been propagating in the north of their country for weeks, and other countries may soon find themselves in the same position. Health-care providers and health departments should anticipate and plan for surges in the demand for hospital services, particularly for intensive care. But state and municipal authorities must also be prepared to undertake social-distancing measures where outbreaks occur.

A carnival attendee wears protective face mask in Venice, Italy, February 2020
A carnival attendee wears protective face mask in Venice, Italy, February 2020
Manuel Silvestri / Reuters

Now is the time to plan for this eventuality and to consider which measures would be most feasible and effective in reducing transmission. Public health agencies should take advantage of the brief, remaining window to determine exactly what should prompt the most drastic measures (for example, school and workplace closures); how to know when the time is right to implement them; and how long they might need to be kept in place. The key to maintaining public compliance and support for social distancing will be to effectively communicate what the plan is and why it is necessary.

Right now, most countries are responding to SARS 2 with containment, which includes travel restrictions or bans and case-based isolation and quarantine. Such measures will not prevent the virus’s spread, but they do buy time, at considerable economic cost. Countries that have not yet been affected, but which will not ultimately be able to prevent local epidemics, must use this time wisely to plan and prepare their communities for the social-distancing measures required to mitigate the impact of SARS 2.

You are reading a free article.

Subscribe to Foreign Affairs to get unlimited access.

  • Paywall-free reading of new articles and a century of archives
  • Unlock access to iOS/Android apps to save editions for offline reading
  • Six issues a year in print, online, and audio editions
Subscribe Now
  • BENJAMIN COWLING is Professor and Co-Director of the World Health Organization Collaborating Centre for Infectious Disease Epidemiology and Control at the University of Hong Kong’s School of Public Health.
  • More By Benjamin Cowling