COVID-19: Insights from OIST＃5 - Tracking the asymptomatic traveler

COVID-19 OIST Insight vol.5

OIST is collaborating with Ryukyu Shimpo for a series of column articles related to COVID-19 on weekly basis. The 5th story was written by Prof. Mahesh M. Bandi.

Article is in Japanese, but please see below the original draft in English.

Tracking the asymptomatic traveler: A COVID-19 detective story
By Dr. Mahesh M. Bandi, Associate Professor, OIST


While nations closed borders in their effort to halt COVID-19, scientists were breaking down scientific boundaries, pooling expertise and data to understand and combat the deadly threat. This is a detective story of how an international team, scattered around the world, pieced together the puzzle of how COVID-19 spread.

Many initial cases were clustered around a seafood market in Wuhan, China, close to the Hankou train station which serves thousands of the city’s 11 million people.

Four initial cases became twelve by the end of December 2019. Doctors were seeing patients with viral pneumonia who did not respond to standard treatment. The clinicians knew little more, but already the outbreak was much larger than they realized. An invisible network of infected people, up to a thousand strong, was moving within Wuhan, passing through Hankou train station each day.

With every person infecting two or three others on average, even a perfect response could not have stopped the spread. China’s officials, however, did not alert the public to this rapidly emerging health risk until December 31st.

The timing was unfortunate. Hundreds of millions were set to travel for the Lunar New Year. Data shows that at least 175,000 people left Wuhan around then. Nearly 7 million people moved in and out of the city, unrestricted, throughout January 2020. By the time Chinese officials acknowledged the risk of human-to-human transmission – on January 21, 2020 – there had been local outbreaks in Beijing, Shanghai and other major cities in China.

While this was happening, international travel remained unaffected. From Wuhan alone, monthly passenger data suggests that 2,200 flew to Sydney, 900 to New York, and more than 15,000 to Bangkok. Indeed, the first COVID-19 case outside China was detected in Bangkok. A 61 year old woman arrived from Wuhan early January, developing symptoms of fever, headache, and sore throat. By January 23rd, early cases were turning up in Tokyo, Singapore, Seoul, Hong Kong and Seattle. Scientists now estimate that around 85% of infected travelers went undetected but remained contagious.

It was only at the end of January that Wuhan was placed under lockdown and airlines canceled flights. By January 31st outbreaks were growing in more than 30 cities across 26 countries – most infections seeded by travelers from Wuhan.

Now, the virus was spreading locally in other parts of the world and by February 14th a pandemic had taken hold.  In early March, thousands of cases were being reported in Italy, Iran and South Korea. China was no longer the main source. In fact, once China started systematically to test, trace and isolate patients, new cases in the country declined dramatically. Similar measures in Singapore, Hong Kong and South Korea also showed it was possible to slow the virus.

In the US, where testing had lagged, President Trump suspended most travel from Europe, but COVID-19 already had a secure foothold. By March 20th, it spread locally in Seattle, New York City and then across the country, outpacing efforts to stop it.

Okinawa’s first infections came from the Diamond Princess liner in early February, but these were effectively controlled. A second round of infections the following month was brought by airline passengers and led to community transmission. Again, the Government’s emergency response stopped the virus from rampaging. For some weeks now, we have not seen infections in the Prefecture, but here in Okinawa we cannot let down our guard. The risk remains, because this virus can travel with people who show no symptoms.