Three-fifths of new coronavirus cases in China showed no symptoms of the illness when they were diagnosed, according to data that is likely to complicate moves by governments around the world to lift strict lockdown measures. A Financial Times analysis of the more complete data into Covid-19 that the Chinese government began publishing at the start of April found that 60 percent of confirmed cases recorded over the past month were non-symptomatic at the time of testing. The prevalence of non-symptomatic cases will be a concern for the authorities not just in China but around the world as they seek to reopen their countries after months of lockdowns. It suggests that large numbers of people are likely to be out in the community spreading the virus without knowing it.
This is a particular worry as many public health experts believe that carriers are at their most infectious in the pre-symptomatic stage of the illness. Alack of testing capacity globally means it is extremely difficult to know how many virus carriers are non-symptomatic. But what evidence there is suggests it is a substantial proportion.
In the Italian town of Vo, which tested all of its 3,300 inhabitants, about half of those initially found to be positive had no symptoms. In Iceland, health authorities found that 43 percent of those infected showed no symptoms at the time of testing. Research by South Korea’s Centers for Disease Control and Prevention into two particulate clusters in the country concluded that the ratio of non symptomatic people was 30 percent to 36 percent.