If true, the figures would further complicate strategies for tackling the pandemic – while underlining the urgency of an antibody test to establish whether or not a person has had the disease in the past. There is also confusion over how many infectious asymptomatic people are – with some scientists challenging the World Health Organisation’s (WHO) claim that transmission in such a way happens only rarely. The classified data – seen by the South China Morning Post – suggests large numbers of people in China had tested positive for coronavirus by the end of last month without displaying any immediate symptoms.
So far there have been more than 300,000 cases of COVID-19 – the illness caused by the coronavirus – worldwide, with more than 14,000 deaths.
However, there are strong indications the actual number could be many times higher, with Government figures suggesting more than 43,000 asymptomatic people tested positive by the last day of February.
This number was not included in the official tally of confirmed cases, which stood at 80,000.
Scientists are divided about what role asymptomatic transmission plays in spreading COVID-19.
A patient usually develops symptoms in five days, although the incubation period can occasionally be as long as three weeks.
The WHO has estimated asymptomatic infections account for one to three percent of cases.
However, in a letter to the International Journal of Infectious Diseases in February, a group of Japanese experts led by Hiroshi Nishiura, an epidemiologist at Hokkaido University, said: “The number of novel coronavirus (COVID-19) cases worldwide continues to grow, and the gap between reports from China and statistical estimates of incidence based on cases diagnosed outside China indicates that a substantial number of cases are under-diagnosed.”
Mr Nishiura put proportion of asymptomatic Japanese patients evacuated from Wuhan, where the illness was first detected, at 30.8 percent – similar to the Chinese government data.
Additionally, data collected from the Diamond Princess cruise ship, quarantined for weeks in Yokohama, Japan, indicates 712 people on board tested positive – of whom almost half, 334, were were asymptomatic.
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Serological surveys will give us an idea of the prevalence of COVID-19
A report on the subject published by specialists from Columbia University, the University of Hong Kong, Imperial College London, Tsinghua University, and the University of California, Davis earlier this year warned: “These undocumented infections often experience mild, limited, or no symptoms and hence go unrecognised, and, depending on their contagiousness and numbers, can expose a far greater portion of the population to the virus than would otherwise occur.”
WHO spokesman Tarik Jasarevic told Express.co.uk: “We don’t know right now; serological surveys will give us an idea of the prevalence of COVID-19.
“Doing serological studies would be useful to better understand the disease.
“Transmission from an asymptomatic person is very rare with other coronaviruses, such as Middle East Respiratory Syndrome coronavirus (MERS-CoV).
“Persons who are symptomatic spread viruses more readily through coughing or exhaling.”
Establishing the true number of people with COVID-19 is a major challenge for the authorities, given how few tests each nation has been able to carry out in comparison with their populations.
Additionally such tests currently can only prove whether or not somebody has the illness currently, rather than whether they have had it in the past.
While on the face of it, a higher proportion of people with COVID-19 in the community might sound like a bad thing, if these people had successfully fought off the illness and were equipped with antibodies, it would potentially leave them equipped with a degree of resistance, experts believe.
Prime Minister Boris Johnson alluded to the significance of such a development last week, when he said during his regular daily coronavirus briefing: “We are in negotiations today to buy a so-called antibody test, as simple as a pregnancy test, that can tell whether you have had the disease.
“It is early days but if it works as its proponents claim, then we will buy literally hundreds of thousands of these kits as soon as practicable because obviously it has the potential to be a total game changer.”
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