Technology

Data from countries with advanced contract tracing measures seem to show the highly contagious virus is not being spread by those who are asymptomatic. The discovery is prompting officials in Singapore to begin easing restrictions.

The spread of coronavirus by those who do not show any symptoms appears to be “very rare”, says a World Health Organization official.
Key points:

  • Contract tracing in some countries has found the spread of coronavirus by asymptomatic people is rare
  • Singapore health officials have suggested half of the country’s cases were symptomless
  • The lack of spread by asymptomatic people could be because they do not cough and sneeze as much

Data from countries with advanced contract tracing measures seem to show the highly contagious virus is not being spread by those who are asymptomatic, according to WHO epidemiologist Maria van Kerkhove.
“It is very rare, and much of that is not published in the literature,” Dr van Kerhove said.
Her comments come after Singapore health officials suggested half of the country’s cases were symptomless after testing measures were ramped up.
The discovery prompted officials in Singapore, which has one of the highest infection tallies in Asia, to begin easing restrictions.
“We have a number of reports from countries who are doing very detailed contact tracing,” Dr van Kerkhove told a WHO media briefing overnight.
“They are following asymptomatic cases, following contacts and not finding secondary transmission.”
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Dr van Kerkhove said the WHO continues to look at reports from counties around the world to confirm how the virus is spread by those who are asymptomatic.
“We are constantly looking at this data and trying to get more information from countries to truly answer this question,” Dr van Kerkhove said.
“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual.”
Singapore’s migrant workers were the victims of the country’s second coronavirus wave.(Reuters: Edgar Su)
She said some cases recorded as asymptomatic are actually mild forms of the disease.
“When we go back [to countries] and see how many of them were truly asymptomatic, we find many have really mild disease,” she said.
“They’re not ‘COVID’ symptoms, meaning they may not have developed a fever yet, may not have a significant cough or shortness of breath.
“Having said that, we know there can be people who are truly asymptomatic.”
A review by a team of Australian scientists found people who did not have symptoms were about a third less likely to spread the disease.
“The reason for that is you’re not sick as long, and also you’re not doing things like coughing or sneezing,” Bond University medical professor Paul Glasziou said last week.
Along with colleagues from the universities of Sydney and NSW, Professor Glasziou compared data from nine international studies to determine what proportion of people with COVID-19 were likely to be asymptomatic.
“About one in six or one in seven will not have any symptoms for the whole of the illness,” Professor Glasziou said.
Dr Maria Van Kerkhove says countries following asymptomatic cases are finding very little secondary transmission.(Reuters: Denis Balibouse)
Dr van Kerkhove stressed how important it was for countries to track symptomatic cases.
“If we actually followed all of the symptomatic cases, isolated them, follow the contacts and quarantine them it would be a drastic reduction in transmission.”