The reproduction rate is a key number in understanding pandemics. The higher the rate, the faster the growth in infected case numbers. A rate of 2.53 was used in the original Doherty Institute modelling published by the federal government on April 7.

This meant that each infected person was assumed to infect an average 2.53 others, leading to case numbers roughly doubling every three days in the absence of policy interventions. The modelling was based on international data as Australian data was not available at that time.