Identifying the infectivity of SARS-CoV-2: an interview with Leo Poon

13 April 2020

Professor Leo Poon Lit-man (Croucher Senior Research Fellowship 2017), the molecular virologist who discovered the first Severe Acute Respiratory Syndrome (SARS) viral sequence, was among the first to identify that the COVID-19 coronavirus is far more contagious from the moment of infection than SARS, potentially making it more difficult to eliminate in humans.

He was also involved in the naming of the new virus, as SARS-CoV-2.

Poon, Professor of Public Health at the University of Hong Kong, was part of a team that took clinical specimens from COVID-19 patients at different stages of infection in Mainland China in the early weeks of the pandemic. While the viral load of SARS patients during the 2003 outbreak generally peaked at about 10 days after onset, the team’s findings, reported in The Lancet Infectious Diseases in February 2020, indicated that COVID-19 samples showed viral loads peaking within the first week of disease onset.

In addition, two patients under active surveillance after being exposed to patients infected with COVID-19 returned positive results before the onset of symptoms, “suggesting that infected individuals can be infectious before they become symptomatic”, the researchers noted.

Poon led the research, with partners at Beijing Centre for Disease Prevention and Control and Beijing Research Centre for Preventive Medicine.

“People assume that it is just like SARS and that is not the case. The virus is more difficult to eliminate in humans because the virus can be transmitted from the beginning. There is a lot of virus in the body day one to seven,” Poon said. That, and the fact that some patients were found to be asymptomatic explained why the virus had spread so fast, he added.

Poon played a leading role in tracking the 2003 SARS outbreak to wild animals and similar interspecies transmission for COVID-19. As part of the Coronavirus Study Group under the International Committee on Taxonomy of Viruses, he has also been involved in developing the official classification of viruses and taxa naming (taxonomy) of the Coronaviridae family, the latest virus being SARS-CoV-2.

Based on its assessment of the phylogeny, taxonomy and established practice, the Group formally recognised the new virus as a sister clade to the prototype human and bat severe acute respiratory syndrome coronaviruses (SARS-CoVs) of the species Severe acute respiratory syndrome-related coronavirus, naming it SARS-CoV-2.

Their Consensus Statement, published in Nature Microbiology in March 2020, after earlier circulation in February, explained that while the Group had responsibility for naming the virus, it was the World Health Organisation (WHO)’s role to name the resulting disease, which it specified as Coronavirus Disease 19, or COVID-19.

This was the third spillover, in only two decades, of an animal coronavirus to humans resulting in a major epidemic, the statement’s authors, including Poon, noted.

Poon was also part of a three-man team from the University of Hong Kong Faculty of Medicine who developed molecular testing enabling rapid diagnosis of COVID-19. The test developed by the team, which included clinical virologist Professor Malik Peiris and virologist Dr Daniel Chu Ka Wing, is now being used in more than 40 countries.

From his earlier research into immunity from the second spillover, Middle East Respiratory Syndrome Coronavirus (MERS), Poon noted that it could not be assumed recovery from COVID-19 would provide lifelong immunity.

It was highly likely those who recovered would not be reinfected in the short term, but it was not known how long that immunity would last, even next winter, he said. There was evidence that after recovery from MERS, first detected in 2012 and with a large outbreak in South Korea in 2015, antibodies dispersed relatively quickly.

The scientist undertook research with a South Korean team into antibody responses of survivors of severe MERS, published in Emerging Infectious Diseases in 2017. The study found that in patients with the highest peak antibody titers, these waned during the first six months, then stabilised over the subsequent six months. But patients who were asymptomatic or had mild symptoms did not develop detectable antibodies. This bore out the findings of other studies that had also found waning antibody titers, the team wrote.

Poon indicated that it would not be easy ban the consumption of wild animals to prevent future spillovers of viruses to humans, even though Mainland China has imposed such a restriction. “In China, people eat a lot of different animals, but this kind of practice can also be found in other countries. I think this is a global issue, it is not just China.”

Without such action, pandemics could re-occur, he said. “We have to prepare for that and such preparation must engage multiple stakeholders from a wide range of disciplines.”



Professor Leo Poon received his doctoral training in Sir William Dunn School of Pathology in University of Oxford (1996-1999). After his graduation, he returned to Hong Kong and worked as a postdoctoral fellow in the Chinese University of Hong Kong (1999-2001). He joined the University of Hong Kong as a Research Assistant Professor in 2001. He currently serves as a Professor in the School of Public Health, HKU. Professor Poon received his Croucher Senior Research Fellowship in 2017.


To view Professor Leo Poon’s Croucher profile, please click here