Comparative analysis of transmission and vaccine effectiveness in Omicron and Delta variant outbreaks in China.

• Omicron BA.2 was transmitted faster than BA.1 and delta. • No significant difference in the effectiveness of vaccines against Omicron BA.1 and BA.2 infections. • Omicron BA.2 can easily break through the existing immune barrier constructed mainly by inactivated vaccines for breakthrough infections in China. • Improving booster vaccination rates, accelerating the availability of non-inactivated vaccines, and treating infections remains a priority. [ABSTRACT FROM AUTHOR]