Press Trust of India

Asymptomatic spread of coronavirus is ‘very rare’, says WHO

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Geneva: The World Health Organization says it still believes the spread of the coronavirus from people without symptoms is “rare,” despite warnings from numerous experts worldwide that such transmission is more frequent and likely explains why the pandemic has been so hard to contain.
Maria Van Kerkhove, WHO’s technical lead on COVID-19 said at a press briefing on Monday that many countries are reporting cases of spread from people who are asymptomatic, or those with no clinical symptoms.
But when questioned in more detail about these cases, Van Kerkhove said many of them turn out to have mild disease, or unusual symptoms.
Although health officials in countries including Britain, the U.S. and elsewhere have warned that COVID-19 is spreading from people without symptoms, WHO has maintained that this type of spread is not a driver of the pandemic and is probably accounts for about 6 per cent of spread, at most.
Numerous studies have suggested that the virus is spreading from people without symptoms, but many of those are either anecdotal reports or based on modeling.
Van Kerkhove said that based on data from countries, when people with no symptoms of COVID-19 are tracked over a long period to see if they spread the disease, there are very few cases of spread.
“We are constantly looking at this data and we’re trying to get more information from countries to truly answer this question,” she said. “It still appears to be rare that asymptomatic individuals actually transmit onward.”
These asymptomatic cases, she said, were identified through contact tracing of known patients and the lack of onward transmission by asymptomatic individuals was based on data from countries carrying out detailed contact tracing. “Much of that has been published in the literature yet,” she said, adding that the agency was reviewing such data to be sure.
Van Kerkhove said such findings were published in a paper from Singapore, where contacts from long-term care facilities and households supported the theory.
Last week, China announced results from its population-wide testing of residents in Wuhan, the epicenter of the outbreak, where they found 300 asymptomatic patients among the city’s 9.98 million residents.
Personal belongings of these asymptomatic carriers such as toothbrushes, mugs, masks and towels have shown negative for the virus in samples collected from the surfaces, Chinese news agency Xinhua reported on Tuesday. A total of 1,174 close contacts of the 300 cases have also been tested negative for coronavirus, the report added.
Experts have sought to ask the WHO to make a distinction between whether the lack of transmission was true only in asymptomatic cases – people with an infection that is so mild that they never have any symptoms – compared to pre-symptomatic cases where people go on to later develop symptoms.
In a study published in the journal Nature in mid-April, researchers from China’s Guangzhou studied 94 patients and estimated that 44% of secondary cases were infected during the index patient’s presymptomatic stage, particularly in settings such as households.
“Disease control measures should be adjusted to account for probable substantial presymptomatic transmission,” they added. (with PTI inputs)


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