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As mentioned several times through this series, much of our initial thinking about SARS-CoV-2 and COVID-19 has been influenced by our long experience with influenza (#37, #46). That’s been useful in some respects, but it has also, at times, made our interpretation of COVID-19 somewhat blinkered. It took us a while, for example, to realise that COVID-19 is both a respiratory and a systemic (viraemic) disease, with virus distributed via the blood directly infecting cells in the heart, kidneys, vascular epithelium and so forth. As a consequence, COVID-19 can present as a primary coagulopathy characterised by small and large blood clots that interfere with oxygen exchange in the terminal alveoli of the lung, or occlude larger vessels and cause strokes. Neither viremia nor vascular blockage are prominent characteristics of the acute stage in human influenza.