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WHO Sparks Fresh Debate on Role of Covid's Silent Spreaders - WHO Changes "rare" position
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Subset of Studies
Van Kerkhove downplayed her comments Tuesday in a live event on social media, saying that she was referring to some unpublished data and two or three published studies that followed people with coronavirus who never developed symptoms, and tried to determine how many additional people they infected.
"That's a very small subset of studies," said Van Kerkhove, head of the WHO's emerging diseases and zoonoses unit. "I used the phrase 'very rare' and I think that's a misunderstanding to state asymptomatic transmission globally is very rare."
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WHO Sparks Fresh Debate on Role of Covid's Silent Spreaders
By
Jeff Sutherland
and
Corinne Gretler
June 9, 2020, 2:08 AM EDT Updated on June 9, 2020, 11:23 AM EDT
• Virus spreaders who never show symptoms appear to be rare: WHO
• Asymptomatic threat has made nations wary of opening economies
https://www.bloomberg.com/news/articles/2020-06-09/who-says-symptomless-spread-is-rare-in-jolt-to-virus-efforts
A World Health Organization official's comment that transmission of the novel coronavirus by people who don't develop symptoms is rare sparked a new debate among infectious-disease experts about the risks of so-called silent spreaders of Covid-19.
"It still appears to be rare that an asymptomatic person actually transmits onward to a secondary individual," Maria Van Kerkhove, head of WHO's emerging diseases and zoonosis unit, said at a briefing in Geneva. She said her comment, which reiterates the group's previous position on so-called asymptomatic cases, was based on detailed reports of contact tracing from various countries.
Although the health organization had said as far back as February that it did not see asymptomatic cases as a major cause of viral spread, Van Kerkhove's remark at a press conference Monday revived controversy over coronavirus transmission routes. Uncertainty over the issue has hindered nations' efforts to re-open battered economies, with the New England Journal of Medicine previously warning that transmission of SARS-CoV-2 by seemingly healthy people is "the Achilles' heel of Covid-19 pandemic control."
Some of the confusion lies in the distinction between the roles played by truly asymptomatic people and those who are merely pre-symptomatic -- and later go on to become ill -- in spreading the disease.
"Comprehensive studies on transmission from asymptomatic individuals are difficult to conduct, but the available evidence from contact tracing reported by member states suggests that asymptomatically-infected individuals are much less likely to transmit the virus than those who develop symptoms," the WHO said in guidance on the use of face masks that it issued last week.
Pre-symptomatic individuals, who develop a higher viral load just before the onset of symptoms, may be infectious, the WHO said. The infection is spread by tiny droplets expelled when infected people sneeze, cough, speak or breathe.
Subset of Studies
Van Kerkhove downplayed her comments Tuesday in a live event on social media, saying that she was referring to some unpublished data and two or three published studies that followed people with coronavirus who never developed symptoms, and tried to determine how many additional people they infected.
"That's a very small subset of studies," said Van Kerkhove, head of the WHO's emerging diseases and zoonoses unit. "I used the phrase 'very rare' and I think that's a misunderstanding to state asymptomatic transmission globally is very rare."
While it's known that some asymptomatic patients can transmit the virus, how many there are and how many are contagious needs further study, Van Kerkhove said. Asymptomatic people tend to be younger and without underlying medical conditions, she said.
Rigid Restrictions
Countries across the globe have been wary of relaxing social-distancing guidelines and rigid travel restrictions, fearing that people without symptoms could spread the Covid-19 pathogen unchecked throughout communities.
"The asymptomatics are still important, particularly if you want to get levels of virus down to very low levels of transmission," said Peter Collignon, a professor of clinical medicine at the Australian National University Medical School in Canberra, who advises the Australian government on infection control.
Because identifying asymptomatic cases is so difficult, the U.S. and other nations have struggled to implement adequate testing to gauge how widespread the disease has become. The Chinese city of Wuhan recently completed the testing of its entire population of 11 million in an effort to identify cases to avoid a resurgence of infections.
Van Kerkhove cited a number of reports from countries doing detailed contact tracing -- in which asymptomatic cases and their contacts were followed -- that found no evidence of secondary transmission. She said countries should focus on following symptomatic cases.
"If we actually follow all the symptomatic cases, isolated those cases, followed the contacts and quarantined those contacts, we would drastically reduce" transmission, she said.
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