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Half of Iceland's COVID-19 spreaders may be asymptomatic, early data suggest

Iceland is giving the world a unique look at how the novel coronavirus that causes COVID-19 is spreading. The Nordic island nation of 360,000 started testing for the virus in early February, and it chose to test both people suspected of having COVID-19 and, notably, people who haven't shown any symptoms. DeCODE, a biotech company working on behalf of Iceland's chief epidemiologist, is testing the general population; so far, it has screened about 9,000 people, or about half of the 17,900 Icelanders tested for the virus, CNN reports.

More than 99 percent of deCODE's volunteer subjects tested negative, but of the roughly 1 percent who tested positive, half said they hadn't shown any symptoms of the disease, company founder Dr. Kári Stefánsson told CNN. "What it means in my mind, is that because we are screening the general population, we are catching people early in the infection before they start showing symptoms." The 50 percent of positive tests from asymptomatic people has been fairly consistent, though the sample is pretty small. DeCODE expects to gather a larger sample of at least 50,000 people, or roughly 13 percent Iceland's population, before the virus peters out.

Other studies have also shown that COVID-19 can be spread by asymptomatic people, and the higher the share of symptomless spreaders, the harder COVID-19 will be to contain. "We now know that asymptomatic transmission likely [plays] an important role in spreading this virus," Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said last week, adding that it's "absolutely clear" asymptomatic infection "surely can fuel a pandemic like this in a way that's going to make it very difficult to control." Having everyone wear face masks outside the home, as the Centers for Disease Control and Prevention (CDC) is considering advising, would be one way to keep asymptomatic transmission at bay.