Department of Information Systems Science, Soka University
Background and Overview
■A state of emergency was declared in Tokyo starting from July 12, 2021, for the 4th time.
■However, the explosive spread of the infection has not stopped. ← Replacement by more infectious Delta variant + Insufficient behavioral change.
■Although the number of infected and severely ill elderly patients has been decreasing, there is a tendency for severe illness to occur among unvaccinated patients in their 40s and 50s.
■An increase in the number of inpatients is causing a tightening of the capacity of the medical system.
■Increase the number of agents to 1 million. Look at the average and standard deviation of 64 trials. ← It will take time, but the gap with reality will shrink.
■The parameters were readjusted to conform to the change in the number of positive cases in Tokyo since December 22, 2020.
■The scenario for replacement with the Delta variant has been adjusted to match the number of positive patients in Tokyo.
#1 When no specific changes are applied to the measure (page 3)
#2 When the same restrictions on behavior as at the time of the previous state of emergency declaration are applied (page 4)
#3 When measures similar to lockdown are taken (page 5)
■Assuming that additional restriction measures on behavior will be implemented over a three-day period beginning August 5.
Simulation Result #1 When no specific changes are applied to the measure
■The average number of positive patients during the peak period was 0.37% of the population = about 50,000 if applied to the population of Tokyo.
■At its peak, 7.7% of the population was infected, or about 1 in 13 people.
■The effectiveness of vaccination will reduce the number of infections, but high levels of infection will persist after November.
Simulation #2 When behavioral restrictions same as those at the previous emergency declaration are applied
■Over a period of 3 days from August 5, behavioral restrictions same as those during the previous emergency declaration in late April were applied.
■Behavioral restrictions slow the rate of spread of infection, but do not lead to a decrease.
■The rebound after the lifting of restrictions results in a large number of infected people at the peak.Slightly lower than the simulation #1 when no special restrictions were applied.
Simulation Result #3: When measures similar to lockdown are taken
■Over a period of 3 days from August 5, strong restrictions on behavior were applied. Zero frequency of gatherings. Travel frequency about 1/10. Social distance cooperation rate 80%.
■Lockdown period is sustained until 2021-end.
■The number of positive patients peaked at 0.073% 8 days after the completion of the lockdown. (Approximately 9,900 people in terms of the population of Tokyo)
■The number of the infected peaked at 1.42% 16 days after the completion of the lockdown. (Approximately 193,000 people in terms of the population of Tokyo)
Insights from the simulation
■The report suggested that the situation could become critical if special measures are not taken promptly.
■Restrictions on behavior during the previous declaration of a state of emergency in late April slowed the increase in the number of infected people, but did not lead to a decrease.
■If we impose restrictions similar to a lockdown, the number of infected people will decrease after about 10 days. However, the peak numbers of positive cases and infected persons, when applied to the population of Tokyo, suggest that the numbers would reach about 9,900 and 193,000, respectively.
■As one of the exit strategies, it is necessary to relax the isolation of infected persons, regardless of whether they have symptoms or not, to some extent.
■Simulations of changes in the number of inpatients and the number of severely ill patients is needed.