Demystifying R naught: Understanding what does it hide?

Since the onset of the pandemic in Wuhan city, China, forecasting and projections of the pandemic are the areas of interest for the investigators, and the basic reproduction rate R0 always stayed the favorite tool. The basic reproduction number (R0) is either ratio or rate or the basic reproductive rate. This dimensionless number was calculated in the past to describe the contagiousness or transmissibility of infectious agents for many communicable diseases. Its importance in the context of COVID-19 is not less, it tells us about the public health measures to be undertaken for disease prevention, and how the transmission of COVID-19 will be affected or eliminated. R0 is affected by several biological, sociobehavioral, and environmental factors which decide agent transmission. R0 is estimated by using complex mathematical models, the results of which are easily distorted, misjudged, and misused. R0 is not a biological constant for an agent or pathogen, it is a rate over time. It can measure the disease severity and also gives an estimate about the herd immunity required for the reversal of epidemic. R0 cannot be altered through vaccination campaigns though it can tell us about the relationship between the population's immune status and epidemic curve. Modeled R0 values are dependent on the model structures and assumptions made. Some R0 values reported in the scientific literature are likely outdated as assumptions are frequently changing in the current pandemic. R0 must be predicted and applied with great caution as this basic metric is far from simple.