Simulations after lifting emergency declaration #2

・Main focus of this simulation
"The number of infected people has been decreasing recently, but how will the infection situation change if the effect of vaccination declines and human flow increases after October?"

➡︎If the number of human flow becomes almost normal:
　Number of infected people may increase even if the effect of vaccination is maintained without declining
　(May exceed medical capacity within a few months after the lifting)

➡︎If the number of human flow is maintained at about 30% less than the normal situation:
　Number of infected people remained flat to increased
　(If the decline of the effect can be ignored, the number of infected people will decrease)

➡︎In both settings of the number of human flow, there is a risk that the infection situation will worsen after January 2022 when 6 months have passed for more than 80% of the elderly population after their 2nd vaccination

➡︎By introducing a vaccine passport to maintain the number of unvaccinated people going out at 50% less than the normal situation, there is a possibility that infection will be contained even if the number of vaccinated people going out returns to normal

・Model for Tokyo based on "Relaxing behavioral restrictions following the spread of vaccination" (released as COVID-19 AI & Simulation Project on August 24)
・Individual attributes: age (in 10-year increments), gender, industry, occupation, frequency of eating out
・Situations of in person contact: homes, schools, workplaces, facilities for the elderly, restaurants, and other contacts with unspecified number of persons
・Individual infection rate and serious illness rate / death rate determined by attributes, situations of in person contact, and number of contacts
・Chiba, Asako. 2021. "The effectiveness of mobility control, shortening of restaurants' opening hours, and working from home on control of COVID-19 spread in Japan" Health & Place 70: 102622.
・Chiba, Asako. 2021. "Modeling the effects of contact-tracing apps on the spread of the coronavirus disease: Mechanisms, conditions, and efficiency" PLoS ONE 16(9): e0256151.
・Reference Kerr et al. (2020)

・At Day 0, the daily number of new positives in Tokyo is about 800 people
・Infectivity of the δ variant (estimated as "infectivity that reproduces the actual number of infected people in a simulation that reflects the most recent human flow and vaccination status")

・Tests
30% of symptomatic patients are tested (test sensitivity 70%)
・Restrictions on outings
Assuming 20%, 30%, or 50% reductions in the number of human flow compared to the situation before COVID-19
・Vaccination
Considering the infection-prevention effect against δ variant and the decline of the effect 6 months after vaccination

・Infection-prevention effect against Delta variant
→　Sensitivity: 15%*, Serious illness rate: 50% (at the completion of the 2nd vaccination, compared to unvaccinated)

・The decline of the infection-prevention effect
　・6 months after the 2nd vaccination, sensitivity decreased to 40% (compared to unvaccinated)
　・Vaccination status at the time of lifting (early October)

(Based on data released by Cabinet Public Relations Office. The number of people vaccinated in September is estimated based on actual results during the month.)
*Bernal, Jamie Lopez, et al. "Effectiveness of Covid-19 vaccines against the B. 1.617. 2 (delta) variant." New England Journal of Medicine (2021).

If the number of human flow is maintained at 30% less than the normal situation: When the effect declines, the number of infected people is flat to slowly increasing (decreasing if the effect is recovered by 3rd vaccination, etc.)

If the number of human flow is increased to 20% less than the normal situation: The infection will increase even if the effect is maintained without decline

If the number of human flow is increased to 20% less than the normal situation: Risk of exceeding medical capacity within a few months after the lifting

If the number of human flow is decreased to 50% less than the normal situation: the number of infected people will rapidly decrease even if the effect declines

The effect of introducing vaccine passport: If the number of human flow of unvaccinated people is set at 50% less than the normal situation, the number of infected people will decrease

・The number of infected people may increase even if the decline of the effect can be ignored
・May exceed medical capacity within a few months after the lifting


・If the infection-prevention effect of vaccination declines, the number of infected people remained flat to increased
・If the decline of the effect can be ignored such as by 3rd vaccination, the number of infected people will continue to decrease

(In either case), there is a possibility that the pace of decrease in the number of infected people will slow down / the pace of increase will speed up around January 2022, 6 months after the majority of the elderly were vaccinated


By introducing a vaccine passport to maintain the number of unvaccinated people going out at 50% less than the normal situation, there is a possibility that infection will be contained even if the number of vaccinated people going out returns to normal

LN(a,b) is the lognormal distribution with expected value a and standard deviation b
Ministry of Health, Labour and Welfare (August 2021 edition),
11 things to know NOW about COVID-19
https://www.mhlw.go.jp/content/000788485.pdf