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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 40%
■Basic reproduction number of the Delta and Omicron variants: 3.75, Efficacy of 2 vaccinations in preventing infection from the Omicron variant: 50% of Delta variant
■Vaccination of the third dose
■February: 700,000 units/week, March: 1 million units/week, pace gradually decreases from April. Final booster vaccination rate = 70% of total population (= 90% of people who are vaccinated the second dose)
■See the next page
■Effectiveness of the third dose for preventing infection: 85%
■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, serious illness rate (metropolitan and national standards), and hospitalization rate during the sixth wave: 20% relative to the 5th wave
■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)
■15,000, 10,000, and 20,000 newly infected patients per day at the end of January
■3 hospitalization standards were considered
■Status quo: Hospitalization for asymptomatic and mild illness, and use of ICU beds “just in case”
■Rather strict: Seriously ill patients (Tokyo): Same as status quo, Seriously ill patients (national): 60% of status quo, overall: 40% of status quo
■Strict: Seriously ill patients (Tokyo): Same as status quo, Seriously ill patients (national): 30% of status quo, overall: 20% of status quo
Vaccination Settings
https://www.mhlw.go.jp/content/10900000/000880779.pdf
Based on the information from the URL above, assumed to vaccinate the third dose at the pace indicated below
January: 150,000 units/week
February: 700,000 units/week
March: 1 million units/week
April: 500,000 units/week
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.
■As for factors not taken into account in the model, see “(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
■A larger wave of infections can be managed with stricter hospitalization standards
■Policy C in “(January 15) Guidelines for COVID-19 Policy during the 6th Wave”: https://covid19outputjapan.github.io/JP/files/Nakata_PolicyOptions_20210115.pdf、https://toyokeizai.net/articles/-/503643
■No traditional behavioral restrictions, medical visits are concentrated on those at high risk of serious illness, compulsory tracking of close contacts and isolation is discontinued, hospitalization is limited to seriously ill patients and moderately ill patients
■“(January 22) Guidelines for COVID-19 Policy during the 6th Wave: Theoretical Background”https://covid19outputjapan.github.io/JP/files/Nakata_PolicyOptionsTheory_20210122.pdf
■Policies that can minimize socioeconomic damage without necessarily increasing the cumulative number of seriously ill patients and deaths in the medium to long term after 2 vaccinations
■Prior to 2 vaccinations, the cumulative number of seriously ill patients and deaths could be reduced without increasing socioeconomic damage in the medium to long term by controlling the spread of infections
■The proposal, “Effective Countermeasures Based on the Characteristics of the Omicron Variant,” from the subcommittee member volunteer on January 21 is in the same direction as Policy C above: https://www.mhlw.go.jp/content/10900000/000885350.pdf
■“The Omicron variant is different from the Delta variant and other COVID-19 infections we’ve seen”
■“Measures should be taken according to the infection risk of the Omicron variant, rather than following the previous 'strong measures’”
■“Concerning moving across prefectures, it is recommended to refrain from activities with a high risk of infection at the destination as described above”
■“Home treatment may possibly be available for younger generation with a low risk of serious illness without visiting a medical institution”
■Local and national governments are also in the same direction as Policy C
■“Tokyo Metropolitan Government to Reduce Surveys of Close Contacts at Public Health Centers (January 20)”: https://www3.nhk.or.jp/news/html/20220120/k10013439931000.html
■“MHLW shifts policy on COVID-19 care: When putting a strain on outpatient care, patients can be tested and treated at home without seeing a doctor (January 24)”:https://www.asahi.com/articles/ASQ1S7G10Q1SULBJ01G.html
Important Points
■A wave of infections cannot be managed with stricter hospitalization standards which is needed for the acquisition of herd immunity
■As in Policy C, cooperation is probably needed from hospitals and clinics that have not treated COVID-19 patients before
■An approach which is closer to Policy C is needed in order to minimize the impact on society by measures such as isolation of close contacts
■Asako Chiba (January 18) and Tatsuo Unemi (January 18) suggested that isolation of close contacts may have a limited effect on controlling the spread of infections when there are many asymptomatic infected persons and asymptomatic close contacts who have not been traced: https://www.covid19-ai.jp/ja-jp/presentation/2021_rq3_countermeasures_simulation/articles/article237/、 https://www.covid19-ai.jp/ja-jp/presentation/2021_rq3_countermeasures_simulation/articles/article231/
■Alternatively, it is necessary to aim to reduce the peak of infections by means of behavioral restriction policies, etc. (which at present have a strong aspect of postponing the acquisition of herd immunity and do not necessarily reduce the total number of deaths in the medium to long term, but have a large impact on socioeconomic activities)
