Explainer: What Is RSV And Why Is It Making So Many People Sick This Winter? Nik Dirga Digital Explainer EditorExplainer: RSV may not quite have the name recognition that influenza and Covid do, but it's actually causing more winter illness. Respiratory syncytial virus - RSV for short - is exceedingly common, particularly in the winter months from May to October. There's plenty of chatter on social media about people suffering long illnesses lately, and much of that could be attributed to RSV, Best said. "There's unfortunately no antiviral treatment for RSV," Bhally said.