The topic was never explored so we don't know if there was no way to know. Instead, epidemiologists just assumed 100% susceptibility, droplet transmission and no seasonality, i.e. that everyone would get infected all at once in one giant wave. This was wrong and also, in contradiction with all pre-existing knowledge of both how coronaviruses work and how SARS-1 worked (SARS-1 was airborne over long distances).