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Wednesday, June 10, 2020, 10:55
WHO now says role of silent virus spreaders remains unclear
By Bloomberg
Wednesday, June 10, 2020, 10:55 By Bloomberg

In this Jan 29, 2020 file photo, Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, speaks during a news conference on COVID-19, at the European headquarters of the United Nations in Geneva, Switzerland. (MARTIAL TREZZINI / KEYSTONE VIA AP)

GENEVA - The World Health Organization (WHO) said it’s still unclear how readily the novel coronavirus is spread by people who don’t develop symptoms, a day after a top official sparked debate by saying such transmission is “very rare.”

Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, said Tuesday that her previous comment had been misunderstood, since she was referring only to certain studies on the spread of COVID-19, involving contact tracing.

While it’s known that some asymptomatic patients can transmit the virus, how many there are and how many are contagious needs further study, Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, clarified

Although the WHO 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 reopen battered economies, with the New England Journal of Medicine previously warning that transmission by seemingly healthy people is “the Achilles’ heel of COVID-19 pandemic control.”

ALSO READ: WHO: Virus spreaders who never show symptoms 'very rare'

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.

“It still appears to be rare that an asymptomatic person actually transmits onward to a secondary individual,” Van Kerkhove said Monday.

Pre-symptomatic individuals, who develop a higher viral load just before the onset of symptoms, may be infectious, the WHO said in guidance on the use of face masks that it issued last week. The infection is spread by tiny droplets expelled when infected people sneeze, cough, speak or breathe.

“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 group said then.

Subset of studies

After Van Kerkhove’s remarks Monday sparked new debate among health experts, she attempted to clarify them Tuesday in a live event on social media.

“I used the phrase ‘very rare’ and I think that’s a misunderstanding to state asymptomatic transmission globally is very rare,” she said.

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.

Speaking at the same event, Van Kerkhove said: "It appears from very limited information we have right now that people have more virus in their body at or around the time that they develop symptoms, so very early on."

She also said preliminary studies suggest that people with mild symptoms can be infectious for up to 8-9 days, and "it can be a lot longer for people who are more severely ill."

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.

READ MORE: Pandemic: WHO warns of higher rates of antimicrobial resistance

“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 US 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.

With Xinhua inputs

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