Document Type : Original Article

Authors

• Kyosuke Ono ¹
• Katsuaki Kikuchi ²

¹ Tokyo Institute of Technology, Tokyo, Japan

² Engineering of Hitachi Co., Ltd., Ottominami, Tsuchiura-City, Ibaraki-prefecture, Japan.

Abstract

Background: It is extremely important to use existing data to study the transition of infection and removal rates, as well as the influence of vaccination, in the major epidemic waves 6, 7, and 8 in Tokyo, and to develop an effective countermeasure to suppress the epidemic.
 Methods: We developed a new IR model of the epidemic in which I and R comprise both symptomatic and exposed individuals. Based on this model, numerical methods were developed to calculate infection and clearance rates, as well as the vaccine effect. To minimize the maximum number of daily positives R_d, we developed a mechanism for controlling the number of people examined T based on the R_d rate. 
 Results: The transitions between epidemic waves 6 and 8, as well as the overall vaccination effect in reducing infection rates, were clarified. Using the measured link between removal rate and tested individuals, the suppressive impact of T control was recreated for waves 6 to 8. As a result, wave 6 showed a significant drop in the maximum R_d from one tenth to one half of the actual data. Although the test system was greatly reinforced in waves 7 and 8, the T control was still able to cut the maximum R_d in half when implemented within 10 days of the epidemic waves' onset.
 Conclusion: The novel IR theory, the calculation method for predicting infection and removal rates, and the T control will all give formidable instruments for future epidemic suppression.

Keywords

• COVID-19
• Epidemiological model
• Epidemic wave analysis
• Vaccination effect
• Tested people number control
• Epidemic countermeasure
• Japan

Main Subjects

• Epidemiology