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■Analysis in Tokyo
■Recovery of “human flow and socioeconomic activities to pre-pandemic levels” taking 6 months from January 2022
■“Behavioral change” and the “functioning of factors not considered in the model” are assumed to start when the critical care bed utilization rate (national standard) exceeds 30%
■Basic reproduction number of the Delta variant: 3.75,
■Basic reproduction number of the Omicron variant: 4.5 (=3.75 x 1.2)
■Third dose: Vaccinated 8 months after the second dose
■Effectiveness of the third dose for preventing infection: 87.5%
■Seasonality: Using the Sine function, the maximum value of the contact rate parameter in winter is set to 1.2 times the minimum value in summer.
■Mortality rate and serious illness rate (metropolitan standards) during the sixth wave (relative to the fifth wave)
■Considered 3 cases: A: 5%, B: 20%, C: 40%
■Refer to “Rates of Serious Illness and Mortality during the Sixth Wave.” Composition effects and decline in effectiveness of vaccination are considered.
■Serious illness rate (national standards) and hospitalization rate during the sixth wave (relative to the fifth wave)
■Considered 3 cases: A: 10%, B: 35%, C: 60%
■Refer to “Rates of Serious Illness and Mortality during the Sixth Wave.” Composition effects and decline in effectiveness of vaccination are considered.
■Considered 3 spread scenarios (using AR1 shocks against the contact rate parameter)
■5,000, 10,000, and 20,000 newly infected patients per day at the end of January
■For further details on the parameters, please refer to “(December 24) Omicron variant” and “Key parameters” found in the latter part of this document.
Important Points
■All scenarios require “behavioral change” and/or “functioning of factors not considered in the model” to reduce infections.
■Depends on the assumption that the efficacy of infection prevention with 2 vaccinations is half for the Omicron variant relative to the Delta variant.
■Refer to “(October 25) Factors behind the infection decrease in Tokyo: Quantitative Analysis.”
■People's risk aversion, behavioral limitations, and the power-law functioning due to a strain on the medical system (scale-free and small-world structure), as well as the functioning of various heterogeneities that are not taken into account in standard models
■If the serious illness rate and hospitalization rate are sufficiently low, there is a possibility that the bed utilization rate will remain below 80% even if the number of newly infected patients per day remains above 10,000 for about a month.
■Although sufficiently decreasing the serious illness rate and hospitalization rate, there may be a situation where critical care beds (national standard) is not enough if the spread of infection is rapid and “behavioral changes and the functioning of factors not considered in the model” are implemented after the bed utilization rate exceeds 30%.
■If the serious illness rate and hospitalization rate are not sufficiently low, there is a possibility that hospital beds are not sufficient for seriously ill patients (national standard) if the number of newly infected patients per day remain at about 10,000 for 1 to 2 weeks,
■This can be said even if the spread of infection is slow (Case C, Optimistic)
■The number of critical care beds (national standard) is more likely to reach the number of secured beds before the number of critical care beds (metropolitan standard).
