Why haven’t lockdowns worked? There are broadly two types of respiratory virus. There are those that spread person to person – like measles – in a continuous chain of transmission, uninterrupted by season and with every susceptible contact falling ill. Then there are those we do not understand so well, like influenza, which are much more complex. Instead of the simplistic close contact model, which assumes Covid spreads like measles, we should perhaps consider an alternative more sophisticated model based on influenza. The influenza virus model is unusual – it is predicated on the majority being exposed to a particular airborne virus but, oddly, only a minority appear to be susceptible to each year’s variant. To complicate matters further, influenza can also spread person to person.