• Six in ten new coronavirus cases may have been caused by covert infections.
  • People with the virus but without symptoms may be spreading infection.
  • Findings underscore the case for stronger measures to keep people apart.
  • The World Health Organization called for more aggressive measures to combat spread.
  • Iceland has tested every one of its citizens, with half of those infected showing no symptoms.

As many as six out of ten cases of coronavirus may be caused by people who suffer mild or no symptoms at all, according to new research.

And those invisible infections may partly explain the rapid spread of the virus. While they don’t show up in the health system or in the official reports, they are key to halting the COVID-19 pandemic.

Scientists have suspected for some time that there is a pool of undiagnosed cases playing a role, especially among people who have not visited any disease hotspots. And this is backed up by some of the first detailed estimates of how the virus may be spreading, according to studies outlined in the journal Nature.

With the pandemic spreading around the globe, the World Health Organization has stepped up it’s rhetoric, calling for a mix of aggressive measures. It has urged nations to “test, test, test” instead of ignoring cases that don’t need urgent attention.

Iceland is doing just that, testing every one of its citizens and while a small proportion have tested positive so far, half of them showed no symptoms.

Even so, many nations are not equipped to conduct mass screenings and with resources stretched testing is often reserved for patients with obvious symptoms. In many countries people with mild symptoms aren’t required to inform the authorities.

The latest studies suggest that people who are infected without showing symptoms may outnumber those officially confirmed as suffering from coronavirus, even in areas where testing has been extensive.

Silently infected

A study using data from Hubei, the province of China that was the epicentre of the original outbreak, estimated that there were 37,400 asymptomatic cases in addition to the 26,000 confirmed cases in early March.

“By our most conservative estimate, at least 59% of the infected individuals were out and about, without being tested and potentially infecting others,” says Wu Tangchun, a public-health expert at Huazhong University of Science and Technology in Wuhan, who led the study.

What is the World Economic Forum doing about the coronavirus outbreak?

Responding to the COVID-19 pandemic requires global cooperation among governments, international organizations and the business community, which is at the centre of the World Economic Forum’s mission as the International Organization for Public-Private Cooperation.

Since its launch on 11 March, the Forum’s COVID Action Platform has brought together 1,667 stakeholders from 1,106 businesses and organizations to mitigate the risk and impact of the unprecedented global health emergency that is COVID-19.

The platform is created with the support of the World Health Organization and is open to all businesses and industry groups, as well as other stakeholders, aiming to integrate and inform joint action.

As an organization, the Forum has a track record of supporting efforts to contain epidemics. In 2017, at our Annual Meeting, the Coalition for Epidemic Preparedness Innovations (CEPI) was launched – bringing together experts from government, business, health, academia and civil society to accelerate the development of vaccines. CEPI is currently supporting the race to develop a vaccine against this strand of the coronavirus.

“This may explain why the virus spread so quickly in Hubei and is now circulating around the world.” Another study of 700 infected schoolchildren in China found that 58% had mild or no symptoms.

Research published in the New England Journal of Medicine traced COVID-19 infections which resulted from a business meeting in Germany attended by someone infected but who showed no symptoms at the time. Four people were ultimately infected from that single contact.

Transmission in Germany of COVID-19
Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany
Image: New England Journal of Medicine

Meanwhile, a study of Japanese evacuees from Wuhan found that a third of those infected with coronavirus did not develop symptoms. Similarly, when passengers from the quarantined cruise ship Diamond Princess were tested, 18% of those infected had no symptoms.

Other research has shown people are most infectious during the early stages of infection. “Some people can be highly contagious when they have mild or no symptoms”, says Michael Osterholm, director of Minnesota University’s Center for Infectious Diseases.

Stay at home

Researchers quoted in Nature say urgent action is needed across the world to slow the rate of infection, calling for the closure of all schools, the cancellation of public gatherings and generally keeping people at home and out of public spaces.

“Implementing strong social-distancing measures is the only way to stop the virus from spreading,” Professor Gerardo Chowell, a mathematical epidemiologist at Georgia State University in Atlanta, told Nature.

You can keep up to date with latest strategic trends, research and analysis on the global COVID-19 pandemic by following the World Economic Forum’s extensive dedicated coverage.