Background
■Supplementary information regarding the results of the simulation on December 1.
・WHO announced a new variant of concern on November 26.
・It may have stronger infectivity than the Delta variant.
・There are concerns about the effectiveness of existing vaccines and medicines.
・The results of tests on those who had already entered Japan from Namibia confirmed that they were infected with the variant in question on November 30.
・Although there are still many unknowns, it is necessary to prepare a variety of possible scenarios that should be assumed through simulations.
Simulation
■The number of agents is 1 million. Look at the average and standard deviation of 128 trials.
■Social activities (including year-end parties, etc.) are assumed to be held the same as last year.
■The final vaccination rate is assumed to be 90% of the target population (about 80% of the total population).
■Assuming the case where 3rd vaccination is not conducted and the case where it is conducted 8 months after the 2nd vaccination.
■After the entry of the Omicron variant into Japan, it is assumed that a small number of infected people are scattered in early December.
■The infectivity is assumed to be 1, 1.5, and 2 times stronger than that of the Delta variant.
■The effects of pre-existing immunity and medicines are assumed to be 25%, 50%, and 75%.
Simulation results #1-1 (without 3rd vaccination)
■In either case, a rapid spread of infections is expected.
■The timing and degree of the expansion depend on differences in infectivity and the effect of pre-existing immunity.
Change in number of positive cases
Simulation results #1-2 (3rd vaccination after 8 months)
■In either case, a rapid spread of infections is expected.
■The difference with no 3rd vaccination is small.
Change in number of positive cases
Simulation results #2-1 (without 3rd vaccination)
■Under the worst-case scenario (double infectivity, 25% preventive effect), the number of new positive cases per day reaches 1.8% of the population.
■The timing and degree of the expansion depend on differences in infectivity and the effect of pre-existing immunity.
Change in number of positive cases
Simulation results #2-2 at peak time (3rd vaccination after 8 months)
■The difference with no 3rd vaccination is small.
Change in number of positive cases
Simulation results #3-1 rise (without 3rd vaccination)
■Our assumption is that the number of new positive cases will gradually increase from mid-December.
■The actual data for Tokyo is similar to the average value and standard deviation if the infectivity is equivalent to the Delta variant.
Change in number of positive cases
Simulation results #3-2 rise (3rd vaccination after 8 months)
■The difference with no 3rd vaccination is small.
Change in number of positive cases
Insights from the simulation
■In a simulation based on the assumption that the Omicron variant has entered the community in mid-December, the actual data from Tokyo were similar to the case where the infectivity is equivalent to the Delta variant.
■If this assumption is correct, it suggests that the period of spread of infections will be in late January.
■Because there are reports that the number of infected people doubled in 2 days in Europe, continuous monitoring is still needed.
Subjects
■As the nature of the Omicron variant becomes clearer, the simulation needs to be conducted again taking into consideration such information.
■Forecasting a strain on hospitals is needed adapting to the rate of serious illness.
Supplemental information
■Details of the simulation→ http://www.intlab.soka.ac.jp/~unemi/SimEpidemic1/info/simepidemic_sim_omicronA2.html
■Details of the simulation model→ http://www.intlab.soka.ac.jp/~unemi/SimEpidemic1/info/simepidemic-model.html
■So that we could conform to the transition of the weekly mean number of positive cases by October 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.
