Effective containment explains sub-exponential growth in confirmed cases of recent COVID-19 outbreak in Mainland China

Benjamin F Maier; Dirk Brockmann

An initial exponential growth of confirmed cases is generically expected for an uncontrolled outbreak and in most cases mitigated with a time delay by effective containment strategies and policies that reduce transmission and effective reproduction of the virus, commonly yielding a saturation in the cumulative case count and an exponential decay in the number of new infections. Although in Hubei the number of cases was observed to grow exponentially in early January [9] , the * [e-mail] subsequent rise followed a sub-exponential, super-linear, algebraic scaling law t µ with an exponent µ = 2.3 (between Jan. 24th and Feb. 9th), cf. Fig. 1A . For the majority of the affected Chinese provinces of Mainland China, however, this type of algebraic rise occured from the beginning, lacking an initial exponential growth altogether. Surprisingly, the exponent µ does not vary substantially with a typical value of µ = 2.1 ± 0.3 for the confirmed case curves in other substantially affected provinces (confirmed case counts larger than 500 on Feb. 12th), despite geographical, socio-economical differences, differences in containment strategies, and heterogeneties that may have variable impacts on how the local epidemic unfolds, cf. Fig. 1B and C.