From the Japan Times:
Omicron should not be underestimated. The variant, which has more than 30 mutations on the spike protein, is said to be at least twice as transmissible as the delta variant, which was likened in contagiousness to the chickenpox by the U.S. Centers for Disease Control and Prevention. That has increased the probability of breakthrough infections even among the vaccinated. Research by Imperial College London recently showed that the risk of reinfection with omicron is 5.4 times greater than with the delta variant, as omicron largely evades immunity gained by past infection or two vaccine doses.