Coronaviruses are respiratory viruses whose appearance on electron microscopy looks like tiny crowns ( ). The first coronaviruses discovered were the cause of pediatric and adult respiratory infections that were not particularly dangerous. One study from Vanderbilt found coronavirus in about 5% of samples from upper respiratory illness and 8% from lower respiratory illness [ ]. Most clinically significant coronavirus infections have been found in children < 2 years of age, as reviewed in this journal in 2009 [ ], although adults also might suffer severe infections [ , ]. This was the picture as late as 2018: a group of respiratory viruses that could cause serious illness in the very young, but with negligible mortality [ , ].
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