The disease experts on Tuesday raised questions about the statement by the World Health Organization claiming that the transmission of the coronavirus or COVID-19 by people with no symptoms is 'very rare', mentioning that this guide could create problems for the government as they look forward to lifting lockdowns.
Maria van Kerkhove, an epidemiologist and also the technical lead on the COVID-19 pandemic for the WHO, stated on Monday that many nations undertaking contact tracing had identified cases that are asymptomatic, but were not detecting they caused the further spread of the novel virus. "It is very rare," she said.
"I was quite surprised by the WHO statement," said Liam Smeeth, a professor of clinical epidemiology at the London School of Hygiene and Tropical Medicine, who added that he had not seen the data Kerkhove's statement was based on.
"It goes against my impressions from the science so far that suggest asymptomatic people - who never get symptoms - and pre-symptomatic people are an important source of infection to others." Officials at the WHO were not immediately available for comment on the subject on Tuesday. Van Kerkhove was due to answer questions at a social media session later on Tuesday.
Experts Raise Questions on WHO Statement
Smeeth and other experts said understanding the risks of transmission among people with mild or no symptoms is crucial as governments begin to ease the lockdown measures they imposed to try and reduce the pandemic's spread and gradually replace them with case tracking and isolation plans.
"This has important implications for the track/trace/isolate measures being instituted in many countries," said Babak Javid, a Cambridge University Hospitals infectious diseases consultant. Some experts say it is not uncommon for infected people to show no symptoms. A non-peer-reviewed study from Germany in May based on 919 people in the district of Heinsberg - which had among the highest death tolls in Germany - found that about one in five of those infected were symptomless.
But data is sparse on how likely such people are to transmit the disease. The co-head of Singapore's coronavirus task force told Reuters on Monday there had been asymptomatic transmission cases there, between people living in close quarters. China said last week that 300 symptomless COVID-19 carriers in its central city of Wuhan, the pandemic's epicentre, had not been found to be infectious.
Keith Neal, a professor of the epidemiology of infectious diseases at the Britain's University of Nottingham, said that while the question of how big a role asymptomatic transmission plays in new infections is unclear, what is known is that people with symptoms are responsible for most of the spread of the disease. "This reinforces the importance of any person who has any of the symptoms of COVID-19 arranges a test ... as soon as possible and isolating until they get their test result," he said.
(With agency inputs)