Ro

I have heard this said as [ar-oh] or as R naught and written as Ro, RO, or R.  The Ro is the reproduction number or measure of how infectious a disease is in a population which has no resistance to it, which is why we are just hearing about it now. It is unusual to have a population with absolutely no resistance to a disease. An Ro of less than 1 shows that the disease is declining. An Ro of 1 means that the rate of infection is stable, but an Ro of more than one indicates that the disease is moving through the population.  COVID-19 has been calculated to have an Ro of 2.8 which means that roughly for every one person that gets it, three more people will get it.  COVID-19 is about twice as infectious as the flu, but not nearly as infectious as measles (Ro 12-18).