Hi CIDD, if you look at any common respiratory virus, it's incredibly obvious that R, if it is to have meaning, must be affected by outdoor temperature. Many studies have shown this - Lidwell J. Hyg., Camb. (1965), 63, 427 was an early {and good} one. Does it make sense to use a model that doesn't include temperature? And is there any other way to explain seasonality? (I say no!) See eg pic of colds in the Netherlands 1925-26 plotted with outdoor temp: oldwivesandvirologists.blog/epidemiology-of-respiratory-illness/
