We argue that the number of infected in the past can be inferred using today's number of deaths and average fatality rate from confirmed cases in the following way:

$$I_{t-j} = \frac{D_t}{{CFR}_t}$$

where $I_t$ = number of infected, $D_t$ = number of deaths, and ${CFR}_t $ = case fatality rate = $\frac{D}{C}$. The $j$ depends on the average number of days that covid patients die after having the first symptoms.