Thic Electron Micrograph Reveals The Morphologic Traits Of The Respiratory Syncytial Virus Rsv. The Virion Is Variable In Shape, And Size Average Diameter Of Between 120 300Nm. Rsv Is The Most Common Cause Of Bronchiolitis And Pneumonia Among Infants And Children Under 1 Year Of Age. (Photo By BSIP/UIG Via Getty Images)