A hospital in Turin, Italy; hundreds of cases of COVID-19 have emerged in the country.Credit: Mauro Ujetto/NurPhoto via Getty

The spread of the new coronavirus could soon become unstoppable, say scientists who are concerned about a rapid surge in the number and size of outbreaks outside China. Some are even muttering the p-word: pandemic.

In South Korea, more than 900 people have been infected, many in an outbreak in the city of Daegu. And in the past few days, officials in Italy have been scrambling to contain a cluster of more than 300 infections in the country’s north that has caused around 10 deaths. Most worryingly, an outbreak in Iran that has killed at least 15 people and has infected an unknown number seems to have already spread the virus to other countries in the Middle East.

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The latest flare-ups — which include many cases with no clear link to China, as well as signs that some went undetected for weeks — could mean that containing the virus, which causes a disease called COVID-19, is no longer possible.

“The identification of previously unrecognized infections in large numbers in Iran and Italy in particular, and also South Korea, really shows us that it’s likely to be impossible to contain coronavirus,” says Ben Cowling, an infectious-disease epidemiologist at the University of Hong Kong.

That could mean that new strategies are needed to curb its spread, scientists say. These include much wider measures outside China that limit social interactions, such as school closures. But researchers need to answer key questions about the outbreak to deploy such measures most effectively. One is whether children transmit the virus as widely as adults do, and whether children are as susceptible to infection.

Pandemic potential?

Officials at the World Health Organization (WHO) in Geneva said on 24 February that the global coronavirus outbreaks do not yet constitute a pandemic — broadly defined as the uncontained spread of an infection in multiple regions. “Does this virus have pandemic potential? Absolutely, it has. Are we there yet? From our assessment, not yet,” said WHO director-general Tedros Adhanom Ghebreyesus. The WHO is sending teams of experts to Italy and Iran to help to control the outbreaks there.

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But other scientists say the surge in international cases marks a tipping point in the 2-month-old outbreak. “Whatever WHO says, I think the epidemiological conditions for a pandemic are met,” says Marc Lipsitch, an infectious-disease epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts. “Under almost any reasonable definition of pandemic, there’s now evidence of it happening.”

For example, community spread is likely to occur in the United States, said an official at the US Centers for Disease Control and Prevention (CDC), in Atlanta, Georgia, in a 25 February press conference. “It’s not so much of a question of if this will happen in this country any more but a question of when this will happen,” said Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases.

The deaths in Iran are particularly troubling, researchers say. “If the first cases identified are fatal cases, that means infections have probably been going on for a few weeks,” says Cowling.

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The discovery in the past week of numerous cases in Lebanon, Iraq and elsewhere that were exported from Iran are worrying, says Andrew Tatem, a geographer at the University of Southampton, UK, whose team has modelled the global spread of the virus. That’s because international travel is not common among most Iranians, indicating that there is likely to be a large number of undetected cases in Iran, where it has been circulating for longer. “I think with Iran, we’re just seeing the tip of the iceberg because we’re only seeing the sickest cases being reported,” adds Devi Sridhar, a public-health researcher at the University of Edinburgh, UK.

Missed contacts

Whether it’s deemed a pandemic or not, Lipsitch and other scientists say that containment measures that seem to have stopped outbreaks from escalating outside of China for more than a month might soon become unfeasible. Those efforts have involved quickly identifying infected people and their close contacts, and isolating them to prevent further transmission. “I don’t see that most places have the resources to track down all the cases that they’ve missed, and the cases that those people infected, and so on,” says Lipsitch.

The WHO’s decision to hold off describing the global outbreaks as a ‘pandemic’ was based in part on data showing that infections in China had peaked between 23 January and 2 February and that control measures, such as the partial lockdown of cities including Wuhan, where the virus originated, had worked to prevent new cases.

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But Cowling says that such measures are unfeasible on a broader scale. A lockdown is likely to be effective only if implemented for weeks or longer, and there is always the risk that easing a quarantine will seed new outbreaks as infected people fan out from cities. “We’ve got to think more carefully about what measures might be sustainable in terms of reducing transmission without shutting down cities completely and stopping people from moving,” he adds.

The role of children

Such mitigation efforts involve ‘social distancing’, which reduces the chances, on average, that people will encounter one another. “I think very soon, most of the world is going to switch to various forms of social distancing, which don’t depend on knowing who’s infectious,” says Lipsitch.

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For instance, studies of the 1918 influenza pandemic1 have found that cities that closed public places such as schools, churches and theatres early in the event experienced lower death rates and fewer overall cases compared with cities that implemented such measures later.

But epidemiologists say too little is known about the current outbreak and the coronavirus to effectively deploy social-distancing measures. More studies are needed to determine the best time to deploy them, says Cowling. One of the most common — school closures — would be worth trying only if scientists knew that children played an important part in the transmission of the coronavirus. There are some reports that children are less likely to experience severe illness when infected, but researchers do not know whether they are as susceptible as adults to infection or whether they easily spread the virus to others. “That’s one of the urgent questions that we need to answer,” says Cowling. Children are important in the spread of both seasonal and pandemic influenza, says Lipsitch, “but in this virus, I think that’s an open question”.

The best way to determine children’s role in transmitting COVID-19, Lipsitch says, would be to analyse closely linked cases, for instance in an individual household, to determine how the virus spread and whether children became infected and passed the virus to others.

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Immunity question

If the coronavirus becomes ubiquitous, and circulates widely in communities, researchers will also want to examine how people develop immunity to the virus after becoming infected. Lipsitch says that researchers are assuming that those infected are immune to reinfection for a certain period — but it’s not clear how long. Immunity isn’t long-lasting following infection with the coronaviruses that cause common colds, he notes, so it might not be long with the new virus. Studies testing antibody levels over time in people who have recovered from the infection could answer that question.

The response to COVID-19 isn’t a matter of either containment or mitigation, says David Heymann, an epidemiologist at the London School of Hygiene and Tropical Medicine. He expects that countries such as Italy and South Korea will try to contain the cases they can and trace their origins, while preparing mitigation measures. “I think that people put way too much emphasis on a pandemic. I think what’s important is a basic understanding of outbreaks and how to deal with them,” he says.