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Questions raised over WHO’s seemingly conflicting COVID-19 advice
The World Health Organization has said asymptomatic spread is ‘very rare’, leading some to ask why it recently advised healthy people to wear a mask when unable to socially distance.
Despite emerging evidence, the WHO has said asymptomatic spread of COVID19 is ‘very rare’. So why has it advised that healthy people wear a mask?
Just days after the World Health Organization (WHO) advised that healthy people wear masks in situations where social distancing is not possible, a WHO official has said that asymptomatic transmission seems to be ‘very rare’.
‘From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,’ Dr Maria Van Kerkhove, head of the WHO’s emerging diseases and zoonosis unit, said during a press briefing in Geneva on Monday 8 June.
‘We have a number of reports from countries who are doing very detailed contact tracing. They’re following asymptomatic cases. They’re following contacts. And they’re not finding secondary transmission onward. It’s very rare.’
However, while Dr Van Kerkhove’s statement resulted in dramatic headlines regarding the seemingly low risk of symptomless carriers spreading COVID-19, infectious disease experts have said more nuanced analysis is required.
Professor Carl Bergstrom, an infectious disease expert at the University of Washington, suggested Dr Van Kerkhove’s statement had been misinterpreted, but also criticised the WHO for its public messaging and said the data used to justify the claim was ‘thin’.
‘The WHO statement pertains to “truly asymptomatic” people who never show classic symptoms, not to pre-symptomatic people who we know can transmit days before showing symptoms,’ he said.
‘Even if truly asymptomatic spread is very rare, pre-symptomatic transmission is likely to be important.
‘What we’ve ended up with here is public health by press release … coupled with poor communications.’
Dr Van Kerkhove’s statements seemed to generate so much confusion because there is
emerging evidence that highlights the sometimes asymptomatic nature of COVID-19 transmission.
In a study published in
JAMA Network Open, researchers found that almost half of 78 patients who tested positive to COVID-19 in Wuhan, China, were found to show no symptoms. While an unrelated study published in
BMJ Journals Thorax found that 104 of the 128 people (81%) on an Antarctic cruise ship who tested positive for COVID-19 had no symptoms.
Professor Ivo Mueller, an epidemiologist at the Walter and Eliza Hall Institute of Medical Research, said such findings suggest the true burden of infection could be as much as ‘five times higher than currently reported’.
While it is possible some cases identified as asymptomatic are actually pre-symptomatic, some cases may only develop mild symptoms – or no symptoms at all.
Dr Van Kerkhove did acknowledge the evidence regarding asymptomatic cases, but said more research and data are needed to know whether asymptomatic carriers play a significant role in widely spreading the virus.
University of Queensland virologist Associate Professor Ian Mackay
previously told newsGP there are many factors that may change the asymptomatic rate, including variation in polymerase chain reaction (PCR) tests and difficulty determining whether someone is truly symptomless, or just pre-symptomatic.
‘There is not just “a” PCR test, there are range of them and they vary,’ he said.
‘I wouldn’t want to be a GP at the moment, having to know how to interpret some of these results. It is tricky.’
The WHO official’s statements have
raised concerns among public health experts who say they can lack clarity and provide conflicting advice, which some believe could lead to the public becoming complacent and less likely to follow recommendations around personal hygiene and social distancing.
The concern follows a record peak of COVID-19 cases, with more than 136,000 cases reported globally on Sunday 7 June – ‘the most in a single day so far’, according to WHO Director General Tedros Adhanom Ghebreyesus.
Dr Van Kerkhove recommended that, for the time being, governments should focus on detecting and isolating symptomatic cases and contact tracing.
‘If we actually followed all of the symptomatic cases, isolated those cases, followed the contacts and quarantined those contacts, we would drastically reduce [the outbreak],’ she said.
But Associate Professor Sanjaya Senanayake, an infectious diseases specialist, says it is too early to rule out the possible significant impact of asymptomatic cases in community transmission.
‘Although we are getting closer to understanding the proportion of asymptomatic cases with COVID-19, we still don’t know for sure the magnitude of the impact that they have on further transmission of cases, ie do they generate lots of secondary cases or only a small proportion?’ he said.
‘There have been varying proportions of asymptomatic cases in differing studies; [for example], about 40% in study from Iceland, 18% on a cruise ship, 30.8% in Japanese evacuees from Wuhan, and almost 80% in another Chinese study. So it’s hard to know which is right.’
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