Objective Omicron (B.1.1.529) variant has caused global concern. Previous studies have shown that the variant has enhanced immune evasion ability and transmissibility, and reduced severity. Methods In this work, we develop a mathematical model with time-varying transmission rate, vaccination and immune evasion. We fit model to reported case and death data, up to Feb 6, 2022 to estimate the transmissibility and infection fatality ratio of Omicron variant in South Africa. Results We found that the high relative transmissibility of Omicron variant is mainly due to its immune evasion ability while the infection fatality rate is substantially decreased. The reduction in the infection fatality rate is about 78.7% (95% confidence interval: 66.9%, 85%). Conclusion Based on data in South Africa and mathematical modelling, we found that the Omicron variant is highly transmissible but with significantly lower infection fatality rate compared to previous variant of SARS-COV-2.
Reduction in the infection fatality rate of Omicron variant compared to previous variants in South Africa