Disease experts on Tuesday questioned a statement by the World Health Organization that transmission of COVID-19 by people with no symptoms is “very rare”, saying this guidance could pose problems for governments as they seek to lift lockdowns.

Maria van Kerkhove, an epidemiologist and the WHO’s technical lead on the coronavirus pandemic, said on Monday that many countries undertaking contact tracing had identified asymptomatic cases, but were not finding they caused further spread of the 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.

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“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.

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