Background
■On February 20, the quasi state of emergency was lifted in five prefectures including Okinawa. In Tokyo and other places, the quasi state of emergency was extended until March 6.
■The supply of tests and hospital beds is still tight and the number of patients with severe illness is tending to increase.
■The positive rate also tends to remain high.
■Although 1 million third vaccinations per day are being carried out nationwide, the overall third vaccination rate is still at 10-plus percent.
Simulation
■We use a multi-agent model that moves in two-dimensional space. The number of agents is one million people.
■Out of the 128 simulations conducted to February 9, we selected eight trials from those close to the trend in the number of positive patients in Tokyo, followed by 16 trials each, for a total of 128 trials.
■It is assumed that the action restrictions will be lifted on March 6, March 20, or April 3.
■The upper limit on the number of tests per day was estimated from the change in the number of tests in Tokyo.The limit is assumed at 0.21% of the population in late January, then falling gradually to 0.138% due to the scarcity of inventories of test kits, etc.
■We ran trials 128 times for each scenario and observed their means and standard deviations.
■The number of positive patients, the number of patients in isolation, the number of people actually infected and the number of patients with severe illness were examined.
Simulation Result #1-1 (Change in Number of Positive Cases)
■The impact of the date of release from action restrictions on the number of positive patients is small.
Simulation Result #2 (Change in Number of Patients in Isolation)
■The impact of the date of release from restrictions is small.
Simulation Result #3 (Change in Number of Actually Infected People)
■The actual number of infected people regardless of whether or not they have symptoms or have had tests at each time point.
Simulation Result #4 (Change in Number of Patients with Severe Illness)
■Under the scenario of the lifting of restrictions on March 6, the number of people with severe illness may increase again.
■Would a release on March 20 mean a slower increase than a release on April 3. .. .???
Insights from the simulation
■We reviewed the parameters and expanded some models based on the recent situation and analyzed cases of the impacts of differences in the extension of the action restriction period.
■If the action declaration is lifted earlier, the number of people with severe illness may increase even if the number of people infected decreases.
■The specific release date needs to be judged based on the revision of assumptions based on trends in various indicators.
Issues
■The number of tests set in the simulation is smaller than the actual number of tests, because the pseudo-symptomatic patients are not included in the test subjects.It is necessary to estimate the number of test recipients with pseudo symptoms and analyze based on the actual number of tests.
■It is assumed that the frequency of gatherings during the action restriction period is constant.It is necessary to analyze the relationship between the degree of relaxation of restrictions and the number of infected people and patients with severe illness.
Supplemental information
■Details of the simulations→ http://www.intlab.soka.ac.jp/~unemi/SimEpidemic1/info/simepidemic_sim_omicronC2.html
■Details of the simulation model→ http://www.intlab.soka.ac.jp/~unemi/SimEpidemic1/info/simepidemic-model191.html
■So that we could conform to the transition of the weekly mean number of positive cases in Tokyo up to February 20, we mainly adjusted the transition of the parameter with the frequency of gatherings and the rate of infectivity, and established a subsequent scenario for its continuation.
