A complete and accurate statistical analysis of cases of contraction with SARS-CoV-2, under the conditions of strict mandatory quarantine and isolation and of a high rate of full vaccination, during the largest COVID-19 outbreaks driven by the Omicron BA.2 subvariant in China are given. SARS-CoV-2 is still new, and little is known about either its directions of variations or its laws of propagation. No country other than China has been able to disclose every case of infection in every epidemic or outbreak since April of 2020. Here, this study reveals that Omicron BA.2 subvariant can still spread very fast and wide in areas with strict “dynamic zero-COVID strategy”1 in China, that there exist cities twenty-fold differences in morbidity rates unrelated to any of the known factors contributing to incidence of infectious diseases, and that Omicron BA.2 subvariant is unpredictable in its virulence, although its severity rate of symptomatic cases is low. This analysis provides first-hand original and valuable information for further research on similar epidemics in the future. It may bring new thoughts for correction of present epidemiological theory and mathematical models. It may also give other countries time to be better prepared for the coming 6th wave driven by Omicron BA.2.